JEE Main/Advanced Revision Notes PDF

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The only app you need to prepare for JEE Main JEE Adv. BITSAT WBJEE MHT CET and more... 4.8 50,000+ 2,00,000+ Rating on Google Play Students using daily Questions available With MARKS app you can do all these things for free Solve Chapter-wise PYQ of JEE Main, JEE Advanced, NEET, BITSAT, WBJEE, MHT CET & more Create Unlimited Custom Tests for any exam Attempt Top Questions for JEE Main which can boost your rank Track your exam preparation with Preparation Trackers Complete daily goals, rank up on the leaderboard & compete with other aspirants 4.8 50,000+ 2,00,000+ Rating on Google Play Students using daily Questions available  GENERAL ORGANIC CHEMISTRY 2 MARKS Co nt en ts 1. Nomenclature 3 2. Isomerism 33 3. Various Effects 75 4. Reaction Intermediateries 96 5. Acids & Bases 122 GENERAL ORGANIC CHEMISTRY  MARKS 3 CL A SSIFICA T I ON OF ORGA N I C COM POUN DS Depending upon the nature of the carbon skeleton, compounds have been broadly divided into two categories. These are : I. Acyclic or Open chain compounds. II. Cyclic or Closed chain compounds. I. Open Chain or Acyclic Compounds : Compounds of carbon having open chain of carbon atoms, branched or unbranched are caled acyclic compounds or aliphatic compounds. Butane CH3 ă CH2 ă CH2 ă CH 3 Isopentane CH3 ă CH ă CH 2 ă CH 3 | CH3 Open chain compounds are also known as aliphatic compounds since the earlier compounds of this class were obtained either from animals or vegetable fats. (Greek, aliphatos  fats). II. Cyclic or Closed Chain or Ring Compounds : Compounds or carbon having closed chain of carbon as well as of other atoms are called cyclic compounds. Depending upon the constitution of the ring, these are further divided into the following categories. 1. Homocyclic or carbocyclic compounds. 2. Heterocylic compounds. 1. Carbocyclic or Homocyclic Compounds : Compounds of carbon having closed chain entirely made up of carbon atoms are called carbocyclic or homocyclic compounds. These are further divided into two groups. (i) Alicyclic Compounds : Closed carbon chains except characteristic benzene ring, resembling in properties with acyclic compounds. For example : cycloalkanes, cycloalkenes etc. Cyclopropane Cyclopentane Cylopenetene Cyclohexene (ii) Aromatic Compounds : Closed chain of only carbon atoms with alternate single and double bonds. For example : Benzene and its derivaties. Some important examples of monocyclic, bicyclic and triclic compounds are GENERAL ORGANIC CHEMISTRY  4 MARKS (a) Monocyclic aromatic compounds : CH3 Benzene Toluene (b) Bicyclic and Tricyclic aromatic compounds : Naphthalene Anthracene (Bicyclic) (Tricyclic) 2. Heterocyclic compounds : Compounds of carbon having closed chain made up of carbon and other atoms. The hetero atoms commonly found in these compounds are oxygen, nitrogen and sulphur but occasionally phosphorus, boron, silicon and some metal atoms like tin, selenium etc. may also be present, Depending upon the chemical behaviour, these are further classified into the following two categories. (i) Alicyclic heterocylic compounds : Aliphatic cyclic compounds containing one or more heteroatoms in their rings are called alicyclic heterocyclic compounds. For example. Tetrahydro Furan Pyrrolidine (THF) O N H (ii) Aromatic heterocyclic compounds : Aromatic cyclic compounds containing one or more heteroatoms in their molecules are called aromatic heterocyclic compounds. For example : (ii Pyridine Furan Pyrrole N O N H GENERAL ORGANIC CHEMISTRY  MARKS 5 Hom ol ogou s Series Organic compounds can be divided into different groups on the basis of similarity in their structure and properties. The property by which a number of organic compounds form a homologous series is termed as homology. The general characteristics of a homologous series are Ć All compounds in the series have the same functional group. Ć All compounds in the series can be represented by the same general formula and can be prepared by the general methods of preparation. Ć All the homologues show a gradual gradation in their physical and chemical properties. Ć Successive members of a homologous series differ by CH2 group and by a mass of 14 units. Table 1.a : Homologous series of aliphatic organic compounds Name of the homologous General formula Functional group IUPAC name Alkanes C nH2n+2 ă (single bond) Alkanes Alkenes C nH2n = (double bond) Alkenes Alkynes C nH2nă2  (triple bond) Alkynes Monohydric alcohols Cn H2n+1 OH ă OH Alkanols Aldehydes Cn H 2nO ă CHO Alkanals Ketones C nH2n O C = 0 Alkanones Monocarboxylic acid Cn H2n O2 ă COOH Alkanoic acids Ethers Cn H2n+2 O CăO-C Alkoxy alkanes Primary amines Cn H2n+1 NH 2 ăNH2 Alkanamines Amides Cn H2n+1 CONH2 ă CONH2 Alkanamides Esters Cn H2n O2 RăCOO ăR Alkyl alkanoate Cyanides Cn H2n+1 CN ăCN Alkane nitriles O Nitro compounds Cn H2n+1 NO2 N Nitroalkanes O Acid chlorides Cn H2n+1 COCl ă COCl Alkanoyl chlorides N o m e n c l a t u r e o f Or g a n i c C o m p o u n d s Nomenclature implies assigning proper name to a particular organic compound on the basis of certain standard rules so that the study of these compounds may become systematic. In the IUPAC system, the name of an organic compound consists of three parts. (i) Word root (ii) Suffix (iii) Prefix GENERAL ORGANIC CHEMISTRY  6 MARKS Wor d Ro o t The word root denotes the number of carbon atoms present in the chain. For example, Chain length Word root Chain length Word root C1 Meth C6 Hex C2 Eth C7 Hept C3 Prop C8 Oct C4 But C9 Non C5 Pent C10 Dec Su f f i x The word root is linked to the suffix, which may be primary, secondary or both. Pr i m a r y s u f f i x It indicates the nature of linkages between the carbon atoms. For example, ane ă for single bonded compounds, ene ă for one C = C bond a diene ă for two C = C bonds a triene ă for three C = C bonds yne ă for one C  C bond a diyne ă for two C  C bonds Se c o n da r y su f f i x It indicates the presence of functional group in the organic compound. For example, Class of organic compound Functional group Secondary suffix Alcohols ă OH ăol Aldehydes ă CHO ă al Ketones C= O ă one Carboxylic acids ă COOH ăoic acid Esters ă COOR alkyl..... oate Acid amides ă CONH2 ăamide Nitriles ă C N ănitrile Amindes ăNH2 ăamine Thioalcohols R ă SH ăthiol Amides R ă CONH 2 ăamide GENERAL ORGANIC CHEMISTRY  MARKS 7 Pr e fi x e s There are many groups, which are not regarded as functional groups in the IUPAC naming of the compounds. These are regarded as substituents or side chains. These are represented as prefixes and are placed before the word root while naming a particular compound. For example, if a compound contains more than one functional group, then one of the functional group is regarded as principal group and is treated as secondary suffix. The other functional groups are regarded as substituents and are indicated by prefixes. Substituent Prefix Substituent Prefix ăC nH 2n+1 Alkyl ăNH2 Amino ăF Fluoro ă NO Nitroso ăCl Chloro ăN=Nă Diazo ăBr Bromo ăOCH3 Methoxy ăI ăIodo ăOC2 H5 Ethoxy ăNO2 Nitro ăOH Hydroxy ăCN Cyano ăCOOH Carboxy ăNC Isocyano ăCOOR Carbalkoxy ăCHO Formyl ăCONH2 Carbamyl ăSH Mercapto ăCO Cl Chloroformyl Thus, a complete IUPAC name of an organic compound may be represented as Prefix + Word root + Primary suffix + Secondary suffix H o w t o N a m e Or g a n i c Co m p o u n d s U s i n g t h e I U PA C Ru l e s In order to name organic compounds you must first memorize a few basic names. These names are listed within the discussion of naming alkanes. In general, the base part of the name reflects the number of carbons in what you have assigned to be the parent chain. The suffix of the name reflects the type(s) of functional group(s) present on (or within) the parent chain. Other groups which are attached to the parent chain are called substituents. Sat u r a t e d H y d r o c a r b o n s Number of Carbons Name 1 methane 2 ethane 3 propane 4 butane 5 pentane 6 hexane 7 heptane 8 octane 9 nonane 10 decane 11 undecane 12 dodecane GENERAL ORGANIC CHEMISTRY  8 MARKS There are a few common branched substituents which you should memorize. These are shown below. CH 3 CH 3 CH 3 CH3 CH 3CH CH 3CH2 CH CH 3 C CH 3CH CH 2 CH 3 isopropyl sec-butyl tert-butyl isobutyl Ru l e s f o r Wr i t i n g I u p a c N a m e s 1. Identify the longest carbon chain. This chain is called parent chain. 6 4 2 7 5 3 4 1 7 5 8 6 1 3 Chain of seven carbons Chain of eight carbons 2 (wrong) (right) Note : If more than one sets of longest possible chains are there, the selected longest chain should have : (1) Maximum number of side chains or 1 3 1 3 5 2 4 2 4 6 5 6 6 atoms chain with two side 6 atoms chain with one side chains or two unbranched chain or one branched side chains is selected side chain is rejected GENERAL ORGANIC CHEMISTRY  MARKS 9 2. If more than one side chain is present, sum of the positions should be minimum while numbering the carbon chain. 2 4 6 8 8 6 4 2 1 3 5 7 9 9 7 5 3 1 sum of positions : sum of positions : 5 + 5 + 7 = 17 3 + 5 + 5 =13 (wrong) (minimum) (right) 3. If two different substituents are at same position from ends, lowest number is assigned in order of their alphabets. Cl Cl 4 1 2 3 3 2 1 4 I I (Right) (Wrong) 4. If a substituent (such as halogen, or nitro group) and a side chain are at same position from opposite ends, lowest number is assigned to substituents CH3 CH3 4 1 2 3 3 2 1 4 Cl Cl (Wrong) (Right) 5. If more than two substituents and side chains are present, the sum of their number should be lowest at the first preference irrespective of the nature of Substituents or side chains. This is referred to as Lowest Sum Rule. GENERAL ORGANIC CHEMISTRY  10 MARKS I I 4 2 2 4 3 3 1 5 5 1 Cl CH3 Br Cl CH3 Br 1 + 2 + 3 + 5 = 11 1 + 3 + 4 + 5 = 13 (Right) (Wrong) Note : In case when starting locant is lower from one side, then lowest sum rule is not obeyed. CH 3 CH3 CH3 CH3 4 6 10 7 5 3 1 2 8 9 7 8 1 3 5 9 10 6 4 2 CH3 CH3 (2 + 7 + 8 = 17 is accepted) (3 + 4 + 9 = 16 is rejected) (methyl gets lower locant i.e. 2) (methyl gets higher locant i.e. 3) 6. If the same substituent occurs more then once, the location of each point on which the substituent occurs in given. In addition, the number of times the substituent group occurs is indicated by a prefix (di, tri, tetra, etc.) E.g. CH3 CH3 CH CH CH3 H3C C CH 3 CH3 CH3 CH3 2-3 Dimethyl butane 2-2 Dimethyl propane In summary, the name of the compound is written out with the substituents in alphabetical order followed by the base name (derived from the number of carbons in the parent chain). Commas are used between numbers and dashes are used between letters and numbers. There are no space in the name. Here are some examples : CH3  CH2 CH3 CH3 CH2 CH3 | | | | CH3  CH2  CH 2  CH  C  CH2  CH3 CH3  CH  CH 2  CH  CH2  CH3 | 5 Ethyl 2 methylhexane CH3 4 Ethyl  3,3dimethylheptane GENERAL ORGANIC CHEMISTRY  MARKS 11 7 6 5 4 3 2 1 CH3  CH2  CH CH  CH CH  CH3 | | | | CH 3 CH3 5' CH2 CH3 C H3 | 6' CH2 CH | 7' CH2 CH2 CH2 2,3,5,Trimethyl 4 propylheptane 1-methylcyclopropane  NOT : 2,3 dimethyl 4 sec butylheptane CH3 CH3 | | 6 5 4 3 2 1 CH3  CH  CH2  CH2  CH  CH2  CH  CH2  CH3 CH3  CH2  CH  CH  CH2  CH3 1 2 3 4 5| 6 7 8 9 | | CH C H3 CH3 CH 2 | | H3C ă CH 2 CH3 2 Ethyl 4  methylhexane 5 Sec  butyl 2, 7 dimethylnonane Ru l e s f o r N a m i n g A l k e n e s a n d A l k y n e s – U n s a t u r a t e d H y d r o c a r b o n s Double bonds in hydrocarbons are indicated by replacing the suffix ăane with ăene. If there is more than one double bond, the suffix is expanded to include a prefix that indicates the number of double bonds present (ăadiene, ăatriene, etc.). Triple bonds are named in a similar way using the suffix ăyne. The position of the multiple bond(s) within ethe parent chain is(are) indicated by placing the number(s) of the first carbon of the multiple bond(s) directly in front of the base name. Here is an important list of rules to follow : 1. The parent chain is numbered so that the multiple bonds have the lowest numbers (double and triple bonds have priority over alkyl and halo substituents) 3 2 4 5 2 3 1 4 5 1 5 carbon chain with (Wrong) 2 unsaturated carbons or one double bond is selected 2. When both double and triple bonds are present, numbers as low as possible are given to double and triple bonds even though this may at times give „ăyne‰ a lower number than „ăene‰. When there is a choice in numbering, the double bonds are given the lowest number. 2 4 6 5 3 1 1 6 3 5 4 2 (Right) (Wrong) GENERAL ORGANIC CHEMISTRY  12 MARKS 3. When both double and triple bonds are present, the ăen suffix follows the parent chain directly and the ăyne suffix follows the ăen suffix (notice that the ÂeÊ is left off, ăen instead of ă ene). The location of the double bond(s) is(are) indicated before the parent name as before, and the location of the triple bond(s) is(are) indicated between the ăen and ăyne suffixes. 5 4 3 2 1 H C C CH 2  C Hă CH 3 2  Penten  4  yne 7 6 5 4 3 2 1 H C  C C CH 2 CH 2 C H=CH 2 1  Hexen  5  yne 4. For a branched unsaturated acyclic hydrocarbon, the parent chain is the longest carbon chain that contains the maximum number of double and triple bonds. If there are two or more chains competing for selection as the parent chain (chain with the most multiple bonds), the choice goes to : (1) the chain with the greatest number of carbon atoms, (2) the number of carbon atoms being equal, the chain containing the maximum number of double bonds. 5. If there is a choice in numbering not previously covered, the parent chain is numbered to give the substituents the lowest number at the first point of difference. Here are some examples : 6 5 4 3 2 1 6 5 4 3 2 1 5 4 3 2 1 CH3 CH CH  CH2  CH CH2 CH C CH CHCH CH2 CH3 CH  CH C CH 1, 4 Hexadiene 1,3 Hexadien 5 yne 3 Penten 1 yne CH2  CH3 CH 3 | 6 |5 4 3 2 1 CH2 4 3 CH3 C  CH2 CH2 CH CH2 6 5 4 |3 2 1 | CH C C  C  CH2  CH2 2 CH 3 | 1 5,5 Dimethyl 1  hexene CH2 CH2 CH3 3,3 Dipropyl  1,3 hexadien 5 yne 1,4,4-Trimethylcyclobutene N a m i n g A l i c y c l i c Co m p o u n d s Aliphatic cyclic compounds are called alicyclic compounds. These compounds are named as follows : Ć The number of carbon atoms in the ring determines the word root. Ć The primary suffix cyclo-is added before the word root. Ć The primary suffix is determined by the nature of the ring (saturated or unsaturated). For cyclic compounds in which ring contains one double bond The suffix -ene is added to the word root. For cyclic compounds in which ring contains a triple bond The suffix-yne is added to the word root. GENERAL ORGANIC CHEMISTRY  MARKS 13 When the ring contains two or three double or triple bonds Suffixes like diene, triene and diyne, triyne are added to the word root. An appropriate suffix or prefix indicates the relevant functional group or any substituent. The position of the functional group or substituent is indicated by the serial number of the carbon atom in the ring to which it is attached. The lowest number to the functional group/substituent is given while numbering of the carbon atoms in the ring. CH2 CH2 H 2C CH-C H3 H2 C C H CH3 H2 C CH | | H 2C CH 2 H 2C  CH 2 methylcyclobutane CH CH2 CH CH 3 cyclopentene 1,3- dimethylcyclohexane CH 2 H2 C C CH · COOH H2 C C H2 C cyclobutyne cyclopropanic acid H a l o a k a n e s (a l k y l h a l i d e s ) General formula : CnH 2n+1 X or RX Prefix : Halo Haloalkanes (or alkyl halides) are monohalogen derivatives of alkanes. They are obtained by replacing one hydrogen atom of alkane molecule by one halogen (X) atom. RH ă H + X (= F, Cl, Br I) RX alkane Haloalkane In the IUPAC system of nomenclature, monohalogen derivative of alkane is named by adding the prefix halo (fluoro, chloro or iodo) to the name of the parent alkane. Halo + Name of parent alkane = Haloalkane The carbon atoms are numbered, if necessary, to show the position of the halogen atom as follows : CH 3l C 2H5Br CH3  CH CH3 CH3ăCH2 ăCH2ăBr | Br Common name : methyl iodide ethyl bromide Isopropyl bromide propyl bromide IUPAC name : iodomethane bromomethane 2-bromopropane 1-bromopropane GENERAL ORGANIC CHEMISTRY  14 MARKS Po l y h a l o a l k a n e s Polyhaloalkanes are those halogen derivatives of alkanes, which contain more than one halogen atom in their molecule. The compounds containing two halogen atoms are termed dihalo and those containing three halogen atoms as trihalo, and so on. The general formula of dihalogen derivatives is CnH2nX 2. In the IUPAC system, a dihalo derivative is named as a dihalogen derivative of the parent alkane, and the positions of halogens atoms are indicated as usual. Polyhalo Parent alkane Name compound Common IUPAC ClH 2CăCH 2Cl Ethane (C2H6 ) Ethylene chloride 1,2-dichloroethane CH3 ă CHBr 2 Ethane (C2H6 ) Ethylidine bromide 1, 1 dibromoethane CHl 3 Methane (CH4) Iodoform triiodomethane A l k a n o l s (Sa t u r a t e d M o n o h y d r i c A l c o h o l s ) General Formula : Cn H 2n+1 OH Functional Group : OH Suffix : ol Alkanols or simply alcohols, are monohydroxy derivatives of alkanes, and are represented by the general CnH2n+1 OH or simply as R-OH. Alkanols or monohydric alcohols are further classified as primary, secondary and tertiary alcohols. The classification is according to the OH group that is attached to a carbon atom, which in turn is attached to one (or more), two or three carbon atoms respectively. For example, H CH3 | | H3 C  C O H H3C  C  OH CH3 CH2 OH | | CH 3 CH3 primary alcohol secondary alcohol tertiary alcohol The IUPAC name of a monohydric alcohol is obtained by replacing the terminal -e from the name of alkane with -ol. No. of Molecular Parent Common IUPAC C- formula alkane name name Atoms 1 CH 3OH CH 4 (methane) Methyl alcohol Methanol 2 CH 3CH 2OH C2H6 (ethane) Ethyl alcohol Ethanol 3 C3H 7OH C3H8 (propane) Propyl alcohol Propanol 4 C4H 9OH C4H10 Butyl alcohol Butanol GENERAL ORGANIC CHEMISTRY  MARKS 15 Name of alkane ă e + ol Name of the alkanol For example : The -OH group can have different positions in alcohols with three or more carbon atoms, leading to the possibility of more than one kind of alcohol. For example in the case of propyl alcohol, following two structures are possible. CH 3 C H CH3 CH3 ăCH2 ăCH2ăOH | OH IUPAC name : 1-propanol 2-propanol Common : n-propyl alcohol isopropyl alcohol (a primary alcohol) (a secondary alcohol) The RO group obtained by removing H atom from the OH group of an alkanol is termed alkoxy group. For example, CH 3O C2H5O C 3 H7 O C4 H9O Methoxy ethoxy propoxy butoxy A l k a n e d i o l s (Di h y d r i c A l c o h o l s ) General formula : Cn H2 (OH)2 Functional group : OH Suffix : diol In the IUPAC system, the name of dihydric alcohol is obtained by adding the suffix diol to the name of the parent alkane and indicating the positions of the -OH groups. Polyhalo Parent alkane Name compound Common IUPAC 2CH OHă1 CH OH Ethane (C2 H6) Ethylene glycol Ethane 1, 2-diol 2 2 3 CH3 ă 2CHOH 1 CH2OH Propane (C 3H 8) Propylene glycol Propane 1, 2-diol A l k o x y a l k a n e s (Et h e r s ) General formula : C nH2n+1-O- CmH 2m+1 or R-O-R´ Functional group : O Prefix : alkoxy Ethers are alkoxy derivatives of alkanes. These are represented by the general formula R-O-R´, where R and R´ are alkyl groups. Ether is termed as simple ether when R and R´ are the same. If the two alkyl groups (R and R´) are different, the ether is termed as a mixed ether. GENERAL ORGANIC CHEMISTRY  16 MARKS When one hydrogen of the alkane is replaced by an alkoxy group, alkoxy-alkanes are obtained. RHăH + OR´ RăOăR´ alkane alkoxy alkoxyalkane In the IUPAC system of nomenclature, the large alkyl group is considered to be the alkane residue, while the smaller alkyl group with oxygen atom is considered to be the alkoxy group. Some typical ethers are named below. Molecular Common Alkane Alkoxy IUPAC formula name residue group name Atoms CH3OCH 3 Dimethyl ether Methane Methoxy Methoxymethane CH2OC 2H 5 Ethyl methyl Ethane Methoxy* Methoxyethane ether C2H5OC 2H5 Diethyl ether Ethane Ethoxy Ethoxyethne * Here the smaller alkyl groups forms the alkoxy group A L K A N A L S ( A L DEH Y DES) General formula : C nH2n + 1CHO or O R C H In IUPAC system of nomenclature, the name of an aldehyde is obtained by replacing the terminal ăe of the parent alkane by the suffix-al. IUPAC name of the aldehyde = Name of the parent alkane ă e + al = Alkanal Names of some individual members Molecular Acid obtained Parent Name formula on oxidation alkane Common IUPAC HCHO HCOOH Methane Formaldehyde Methanal (formic acid) CH3CHO CH 3CHOOH Ethane Acetaldehyde Ethanal (acetic acid) C2H5CHO C2 H5COOH Propane Propionaldehyde Propanal (Propionic (acid) Since the ăCHO group is always present at the end of the chain in aldehydes there is no need to designate its position 1. GENERAL ORGANIC CHEMISTRY  MARKS 17 While counting the carbon atoms in the parent chain, the carbon of the ăCHO group is also counted. For example, the parent chain in CH3CH 2CH2 CHO consists of four C atoms and not three. Hence, CH3 CH2 CH2CHO should be named as butanal and not 1-butanal as -CHO is always at the end of the chain (i.e., -CHO carbon is always at position 1). A L K A N ON ES (K ET ON ES) General formula : (C nH 2n+1. CO. C m H2m+1) Functional group : CO or R-CO-R´ Suffix : one The following general formula describes Ketones (or alkanones) R C = O where, R and R´ are alkyl groups. R The two alkyl groups (R and R´) may be same or different. When the two alkyl groups (R and R´) are same, the ketone is a simple ketone. If the two are different the ketone is called a mixed ketone. The IUPAC name of an alkanone is obtained by replacing the last -e from the name of the parent hydrocarbon with the suffix - one. The position of the carbonyl group is indicated by a numeral referring to the serial number of the carbon atom bearing the carbonyl group in the chain. The numbering is done so as to give the carbonyl group the lowest number. IUPAC name of ketone = Name of parent alkane ăe + one = Alknone No. of Molecular Alkyl groups Parent Common IUPAC C- formula attached to name name Atoms the > CO group 3 CH3ă CO ă CH 3 Methyl, Methyl Propane Dimethly ketone Propanone 4 CH3ă CO ă CH 2 CH3 Methyl, Ethyl Butane Ethyl methyl Butanone-2 ketone 5 CH3CH 2 ăCOăCH2 CH3 Ethyl, Ethyl Pentane Diethyl ketone Pentanone-3 Alk o nic Ac ids or sat urat ed m onoc arbox ylic ac id General formula : CnH2n + 1 COOH O Functional group : R  C OH Suffix : oic acid GENERAL ORGANIC CHEMISTRY  18 MARKS On replacing one H atom of an alkane by one carboxylic (- COOH) group a saturated monocarboxylic acid or alkanoic acid is obtained. Higher members of this family are generally, known as fatty acids (obtained by the hydrolysis of fats). In IUPAC system, the name of an alkanoic acid is obtained by replacing the last ÂeÊ from the name of the parent alkane with -oic acid. Name of monocarboxylic acid = Name of the parent alkane -e + oic acid = Alkanoic acid Typical members are named below : No. of Molecular Parent Common IUPAC C- formula alkane name name Atoms 1 HCOOH Methane Formic acid Methanoic acid 2 CH3COOH Ethane Acetic acid Ethanoic acid 3 CH3CH2 COOH Propane Propionic acid Propanoic acid 4 CH3CH2 CH2 COOH Butane Butyric acid Butanoic acid 5 CH3(CH2 )3COOH Pentane Valeric acid Pentanoic acid A l k a n e d i o i c a c i d s (Sa t u r a t e d d i c a r b o x y l i c a c i d s ) General formula : C n H 2n+2 (COOH) O Functional grooup : C OH Suffix : dioic acid A dicarboxylic acid contains two carboxylic groups linked to the same or different carbon atoms. In the IUPAC system, the name of alkanedioic acid is obtained by adding the suffix, -dioic acid to the name of the parent alkane. Name of the dicarboxylic acid = Name of the parent alkane + dioic acid = Alkanedioic acid For example : Ethanedioic acid (oxalic acid, parent alkane is ethane) COOH | COOH Propanedioic acid (Malonic acid, parent alkane is propane) COOH H2 C COOH GENERAL ORGANIC CHEMISTRY  MARKS 19 Butanedioic acid (Succinic acid, parent alkane is butane) H2 C COOH H 2C COOH A l k a n a m i d e s (A c i d A m i d e s ) General formula : C nH2n + 1 CONH2 where n = 0, 1, 2... Functional group O O C R C NH 2 or NH2 Suffix : amide In IUPAC system, the amides are named by replacing the letter e of the parent alkane by the word amide. IUPAC name of acid amide = Name of the parent alkane - e + amide = Alkanamide Typical amides are named below : Molecular Parent acid Parent alkane Common name IUPAC name HCONH2 HCOOH (formic acid)* Methane Formamide Methanamide CH3CONH 2 CH 3COOH (acetic acid)* Ethane Acetamide Ethanamide CH3CH2 CONH2 C 2H 5COOH Propane Propanamide Propanamide (propionic acid)* * Common names of the acid. A l k a n e n i t r i l e s (A l k y l C y a n i d e s ) General formula : R-C  N Functional group : C  N Suffix : nitrile The IUPAC name of an alkyl cyanide is obtained by adding the suffix - nitrile to the name of the parent alkane. Thus, an alkyl cyanide is alkanenitrile in the IUPAC system. Some common alkane nitriles are : Molecular Acid formed Parent Common IUPAC formula on hydrolysis alkane name name HăC  N HCOOH (formic Methane Hydrogen Methanenitrile acid) cyanide H3 ă C  N CH3COOH Ethane Methyl Ethanenitrile (acetic acid) cyanide GENERAL ORGANIC CHEMISTRY  20 MARKS A l k a n o y l c h l o r id e s (A c i d Ch l o r i d e s ) General formula : CnH2n+1 COCl where n = 0, 1, 2... Functional group : O O C R C Cl or Cl Suffix : oyl chloride Acid chlorides contain the functional group ăCOCl. This functional group is obtained by replacing the ăOH group of a carboxyl group with a chloride atom. The IUPAC name of an acid chloride is obtained from the IUPAC name of the parent acid by replacing the terminal e of the parent alkane by oyl chloride. IUPAC name of the acid chloride = Name of the parent alkane - e + oyl chloride = Alkanoyl chloride Some acid chlorides are named below, Methanoyl chloride : (formyl chloride, parent acid is Methanoic acid) HCOCI Ethanoyl chloride : (acetyl chloride, parent acid is Ethanoic acid) CH3 COCI A l k a n o i c a n h y d r i d e s (a c i d a n h y d r id e s ) O O || || General formula : R  C  O  C  R O O || || Functional group :  C  O  C  Suffix : oic anhydride An acid anhydride may be considered as the condensation product of two molecule of a monocarboxylic acid obtained by losing one molecule of water. RCOOH RCO O - H2 O RCOOH RCO IUPAC name of an acid anhydride = IUPAC name of acid parent acid-acid + anhydride = Alkanoic anhydride H3 C CO O H3 C CO For example, Ethanoic anhydride (acetic anhydride, parent acid is ethanoic acid) GENERAL ORGANIC CHEMISTRY  MARKS 21 A l k y l a k a n o a t e s (e s t e r s ) O || General formula : R  C  OR ' O || Functional group :  C  OR' Suffix : oate An ester contains the group COOR where R is an alkyl group. The hydrolysis of the ester gives the parent acid and so its name is based on the name of the acid. Name of an ester = Alkyl group from the alcohol + Name of the parent acid - oic cid + oate The names of some typical esters are Molecular Common system IUPAC system formula Parent acid Name of ester Parent acid Name of ester HCOOCH3 Formic acid Methyl formate Methanoic acid Methyl methanoate CH3COOCH 3 Acetic acid Methyl acetate Ethanoic acid Methyl Ethanoate Nit roa lk an es a nd Alk y l Nit rit es O General formula : R · N O O Functional group : · N O Prefix : nitro No. of Molecular Parent Common IUPAC C- Atoms formula alkane name name 1 CH3 NO2 Methane Nitromethane Nitromethane 2 CH3 CH2NO2 Ethane Nitroethane Nitroethane 3 CH3 CH2CH 2 NO2 Propane n-Nitropropane 1-Nitropropane CH 3CHCH 3 4 | Propane iso-Nitropropane 2-Nitropropane NO2 Nitro compounds are named as the nitro derivatives of the parent alkane in both the systems of nomenclature. This is done by adding the prefix nitro to the word root of the parent alkane. GENERAL ORGANIC CHEMISTRY  22 MARKS Alkyl nitrites General formul : R-O-N=O Functional group : ăO-N=O Alkyl nitrites are named by adding the suffix nitrite to the alkyl group. For example CH3-O-N=O is Methyl nitrite. C2H5-O-N=O is Ethyl nitrite. Al k an a m ine s (A m i n e s) Amines are formed by replacing one or more hydrogen atoms of ammonia (NH3) with alkyl groups. These are further classified as primary, secondary and teritary amines according to one, two or three hydrogen atoms of ammonia being replaced by alkyl groups. For example, Primary (amino, NH 2) RăNH2 Secondary (imino, NH) R NH R Tertiary (nitrile,N) R R N R In IUPAC system, primary aliphatic amines are named as alkanamine. This is done by replacing the ÂeÊ of the parent alkane by the suffix amine. The secondary and tertiary amines are named as alkyl derivatives of the primary amine. The higher alkyl group is considered as the residue of the parent alkane. Examples of the amines : No. of Molecular Parent Common name IUPAC name C- Atoms formula alkane H3C NH 1* Methane Dimethylamine N-methylmethanamine H3 C H5C 2 NH 2* Ethane Ethymethylamine N-methylethanamine H3 C H3 C H3C N Methane Trimethylamine N,N-dimethylethamine C 2 H5 * This indicates the number of C-atoms in the chain : the other groups are considered as the substituent. GENERAL ORGANIC CHEMISTRY  MARKS 23 Primary amines No. of Molecular Parent Common IUPAC C- Atoms formula alkane name name 1 CH3 NH2 Methane Methylamine Methanamine 2 C2H 5NH 2 Ethane Ethylamine Ethanamine 3 C3H 7NH 2 Propane Propylamine Propanamine 4 C4H 9NH 2 Butane Butylamine Butanamine For primary amines containing three or more carbon atoms, there can be more than one isomers of the concerned amine. For example, there are two propylamines. H 3C  CH CH 3 H3C  CH 2  CH 2  NH2 | 1propanamine NH2 2 propanamine A l k a n e n i t r i l e s (A l k y l C y a n i d e s ) Geneal formula : R-N-C  N Functional group : C  N Suffix : nitrile The IUPAC name of an alkyl cyanide is obtained by adding the suffix - nitrile to the name of the parent alkane. Thus, an alkyl cyanide is alkanentrile in the IUPAC system. Some common alkane nitriles are : Acid formed Parent Common IUPAC name Molecular on alkane name formula hydrolysis HăC  N HCOOH (formic Methane Hydrogen Methanenitrile acid) cyanide H3 C ăC  N CH3COOH Ethane Methyl Ethanenitrile (acetic acid) cyanide A l k y l c a r b y l a m i n e s (A l k y l I s o c y a n i d e s ) General formula : R · N C Functional group : · N C Suffix : Carbylamine In the IUPAC system, these compounds are named as carbylamines of alkyl groups attached to the ăNC group. GENERAL ORGANIC CHEMISTRY  24 MARKS Molecular Acid formed on Common IUPAC name formula hydrolysis name CH 3 ăNC CH3COOH Methyl Methyl (acetic acid) isocyanide carbylamine C2H 5ăNC C2H5 COOH Ethyl Ethyl (propionic acid) isocyanide carbylamine Ru l e s f o r N a m i n g Or g a n i c Co m p o u n d s Co n t a i n i n g On e o r M o r e Fu n c t i o n a l Gr o u p s The rules for naming an organic compound containing functional groups are exactly same as discussed already for compounds containing double and triple bonds. In this case, the preference of lowest number is given to carbon atom bearing the functional group. The rules are summarized below : (i) Select the longest continuous chain containing the carbon atom having functional group(s). (ii) The numbering of atoms in the parent chain is done in such a way that carbon atom bearing the functional group gets the lowest number. (iii) If two or more same functional groups are present, these are indicated by using di, tri, tetra as prefixed to the name of the functional group. (iv) If the organic compound contains a functional group, multiple bonds, side chain or substituents, the following order of preference must be followed, Functional group > Double bond > Triple bond > Side chain. (v) When an organic compound contains two or more functional groups, one group is regarded as the principal functional group and the other group is treated as the secondary functional group, which may be treated as substituent(s). The following order of preference is used for selecting the principal functional group, Carboxylic acids > sulphonic acids > acid anhydrides > esters > acid chlorides > amides > nitriles > aldehydes > ketones > alcohols > amines > imines > ethers > alkenes > alkynes. Different classes of functional groups including multiple bonded compounds and the suffix or prefix required to name these compounds are given in the preferential decreasing order in the following table. Class of compounds Functional group or Suffix Prefix substituent 1. Carboxylic acids C= O Carboxylic acid/oic acid Carboxy HO O || 2. Sulphonic acids  S  OH Sulphonic acid sulfo || O GENERAL ORGANIC CHEMISTRY  MARKS 25 O O || || 3. Acid anhydrides C O  C oic anhydride · 4. Esters C =O (R)... carboxylate alkoxy carbonyl RO /(R)... oate 5. Acid halides C=O Carbonyl halide/oyl halo carbonyl X halide 6. Amides C=O Carboxamide/amide carbamoyl NH2 7. Cyanides ă CN Carbonitrile/nitrile cyano 8. Aldehydes C= O Carbaldehyde/al formyl/oxo H 9. Ketones C= O one keto/oxo 10. Alcohols ăOH ol hydroxy 11. Amines ăNH2 amine amino 12. Imines = NH imine imino 13. Ethers ă C ă O ă C ă ă alkoxy 14. Alkenes = (double bond) ene · 15. Alkynes  (triple bond) yne · For those functionalities, which have two prefixes and/or suffixes, the first one is used when carbon atom of the functional group is not a part of the longest continuous chain and the second one is used, when carbon atom is counted in the longest chain. GENERAL ORGANIC CHEMISTRY 26 MARKS Some Examples (1) (HOCH 2CH 2O)2 CHăCO2 H Bis(2ăhydroxyethoxy) ethnaoic acid C 2H 5 1 2 3 (2) 4 1ăEthylă4ămethylcyclohexane CH3 F F CH3 CHăCH CH2CH3 (3) CH3(CH2) 4CH2CHCH2CH(CH2)3CH3 7 ă (1, 2 ă Difluorobutyl) ă 5 ă ethyldecane O || (4) CH 3 CH 2 CH2  C  CH 2Cl 1ăchloropentană2ăone 5 4 3 2 1 2 1 (5) CH CH  O  CH CH Cl 1ăChloroă2ăethoxyethane 3 2 2 2 (6) OHCCH 2CH 2 CH CH2CHO 3ă(Formylmethyl)hexanediă1, 6ăal | CH2CHO 4 3 2 1 (7) OHCCH2CH2CH  CH2CHO Butaneă1,2,4ătricarbaldehyde | CHO (8) CH3CH2 CH OCH2CH3 1, 1ăDiethoxypropane | OCH2CH3 (9) HO2 CCH2 CH2 CH C H2CH2CO2 H Pentaneă1,3,5ătricarboxylic acid | CO2H (10) NCCH 2CH 2CH 2CH  CH 2CH 2CN Hexaneă1,3,6ătricarbonitrile | CN (11) CH3CSăOăCOCH2 CH 3 Propionic thioacetic anhydride O || (12) CH3  C CH2 CH2CH2 CO2H 5ăOxohexanoic acid 6 5 4 3 2 1 O O || || (13) CH3 CH2  C  CH2  C  CH3 Hexane ă2,4ădione 6 5 4 3 2 1 (14) CH2=CHCH 2CH(OH)CH3 Pentă 4ăen ă2ăol GENERAL ORGANIC CHEMISTRY  MARKS 27 Na m i n g A l i c yc l ic & Ar o m a t ic Co m op ou nd Ć If alcicyclic group is attached to the long chain, the chain is numbered from the side of the alcicyclic group. 7 5 3 1 8 6 4 2 Ć Cycloalknes with only one ring are named by attaching prefix cyclo-to the names of the alkanes possessing the same number of carbon atoms. cylopropane cyclopentane Ć If only one substitutent is present, it is not necessary to designate its position. OH Cl cyclohexanol isopropylcyclohexane chlorocyclohexane Ć When two substituents are present, we number the ring beginning with the substituent first in the alphabet. When three or more substituents are present, we begin with the substituent that leads to the lowest set of locants. CH3 CH3 CH2 CH3 1 2 3 4 CH2CH3 Cl 1-ethyl-3-methylcyclohexane 1-ethy 1-3 methylcyclohexane not 1-ethy l-5 cyclohexane not 1-ethy l-5 cyclohexane GENERAL ORGANIC CHEMISTRY 28 MARKS Ć When a single ring system is attached to a single chain with a greater number of carbon atoms, or when more than one ring system is attached to a single chain, then they are named as cyclocalkanes. 1-cyclobutylpentane 1,3 dicyclohexylpropane Ć Cycloalkanes consisting of two rings only and having two or atoms in common are named by taking the prefix bicyclo followed by the name of the alkane. In between bicyclo and alkane, number of carbon atoms representing the bridge (except bridge head positions) are written with in bracket. Bridge head positions are those which join two rings. 7 C1 and C4 are joined 4 to bride of one carbon atoms 1 3 5 { 2 6 { C1 and C2 are joined C1 and C4 are joined to bride of two carbon atoms to bride of two carbon atoms It is alicyclic compund with seven carbon atoms, hence it is bicycloheptane. The two rings have two C-atoms in common, (numbered 1 and 4) in structural formula. These positions are called the bridgehead positions. Carbon atoms 1 and 4 are tied together by three bridges of two, two and one carbon atoms. Hence, it is bicyclo [2, 2, 1] heptane (norbornane). 7 4 1 5 3 2 6 bicyclo [2, 2, 1] hept-2-ene bicyclo [2, 2, 0] hexane bicyclo [4, 4, 0] decane GENERAL ORGANIC CHEMISTRY  MARKS 29 9 2 1 3 H3 C 8 6 4 7 5 bicyclo [2, 1, 1] hexane bicyclo [1, 1, 1] pentane 8-methy bicylo [4, 3, 0] nonane 2 1 7 8 CH3 3 6 5 4 8 methyl bicyclo [3, 2, 1] octane Ć Spiranes are polycyclics that share only one C. Spiro is written before the alkane. spiro [4, 3] octane spiro [5, 2] octane Ć For naming aromatic compounds, no special rules are needed to name them, but they are named as substituted benzene. CH3 CH3CHCH3 CH CH2 methylbenzene ispropylbenzene vinylbenzene Cyclopropyl (toluene) (cumene) (styrene) (benzene) GENERAL ORGANIC CHEMISTRY  30 MARKS Ć When large and complex groups are attached to the benzene ring it is common practice to name the molecule as an alkane, alkene, etc., and benzene as side chain derivative written as pheny 1 (C 6H 5, ·,Ph). CH3CHCHO · C CH · CH2 ·  phenylbenzene or phenylethyne 2-phenylpropanal diphenylmethane biphenyl Fo r Ar o m a t ic r in g X (1) (6) (2) (3) (5) (4) Let there is an element on position 1. We do numbering of other positions, after defining the no. 1 position. There are specific name for different positions. position 1, 2 and 6 Ortho (o) position 3 and 5 meta (m) position 4 para (p) NO2 NO2 Cl Cl m-choro nitro benzene Oăcholro nitro benzene NO2 Cl (p-chloro-nitrobenzene) GENERAL ORGANIC CHEMISTRY  MARKS 31 Ex a m p l e s 1. Phenol CH2 CH 3 2. EthylBenzene Cl 3. Chlorobenzene OH 4. Phenol OH 5. 3-Chlorophenol Cl OH CH2 CH CH2 CH 3 6. 1-phenylButană2ăol 7. H3 C CH CH2 CH3 2-ButylBenzene O 8. CH2 C CH 3 1-phenylpropan ă2ăone GENERAL ORGANIC CHEMISTRY 32 MARKS CHO 9. Benzaldehyde COOH 10. Benzoic acid CH O 11. 4-aminobenzaldehyde NH2 C OO H 12. OH 3-hydroxy benzoic acid CO NH2 13. Benzanamide 14. N H Năphenylbenzenamine O 15. C NH CH3 N-methylbenzenamide O NH C CH 2 CH3 16. N-phenylpropoanamide GENERAL ORGANIC CHEMISTRY  MARKS 33 I SOM ERI SM In the study of organic chemistry we come across many cases when two or more compounds are made of equal number of like atoms. A molecular formula does not tell the nature of organic compound; sometimes several organic compounds may have same molecular formula. These compounds possess the same molecular formula but differ from each other in physical or chemical properties, are called isomers and the phenomenon is termed isomerism (Greek, iso = equal; meros = parts). Since isomers have the same molecular formula, the difference in their properties must be due to different modes of the combination or arrangement of atoms within the molecule. Broadly speaking, isomerism is of two types : I. Structural isomerism : When the isomerism is simply due to difference in the arrangement of atoms within the molecule without any reference to space, the phenomenon is termed structural isomerism. In other words, while they have same molecular formula they possess different structural formulas. This type of isomerism which arises from difference in the structure of molecules, includes : (i) Chain or Nuclear Isomerism; (ii) Positional Isomerism (iii) Functional Isomerism (iv) Metamerism and (v) Tautomerism II. Stereoisomerism : When isomerism is caused by the different arrangements of atoms or groups in space, the phenomenon is called Stereoisomerism (Greek, Stereos = occupying space). The stereoisomers have the same structural formula but differ in the spatial arrangement of atoms or groups in the molecule. In other words, stereoisomerism is exhibited by such compounds which have identical molecular structure but different configurations. Stereoisomerism is of three types : (a) Geometrical or cis-trans isomerism; and (b) Optical Isomerism (c) Conformational isomerism Thus various types of isomerism could be summaried as follows : ISOMERISM STRUCTURAL ISOMERISM GEOMETRICAL OPTICAL CONFORMER ISOMERISM ISOMERISM ISOMERISM GENERAL ORGANIC CHEMISTRY  34 MARKS CH A I N I SOM ERI SM This type of isomerism arises from the difference in the nature, structure of the carbon chain. For example, for butane (C 4H10), the following arrangements are possible. (a) Butane (C4 H 10) H3 C  CH  CH3 | H3 C  CH2  CH2  CH3 CH3 n-butane (butane) iso-butane  2-methylpropane  (straight chain) (branched chain) (b) Pentane (C5 H12) CH3 H3C HC CH 2 CH3 | | H 3C  C  CH 3 H3 C  CH2  CH2  CH2  CH3 CH3 | CH3 n-pentane iso-pentane (neo-pentane (2-methylbutane) (2,2-dimethylpropane) (c) Butanol (butyl alcohol) H3CHCCH 2OH | CH3 H3CăCH2 ăCH2 ăCH2 ăOH isobutyl alcohol (butan-1-ol) (2-methylpropanol-1) POS I T I ON I SOM ER I SM This isomerism arises due to the difference in the position of the same functional group or the same substituent while the arrangement of carbon atoms remains same. For example, (a) Chloropropane (C3H7Cl) H3 C  C H  CH3 H3 C  CH2  CH2  Cl | (n-propyl chloride) Cl (1-chloropropane) (iso-propylchloride) (2-chloropropane) (b) Butene (C4H 8) H2 C  CH  CH2  CH3 H3 C  CH  CH  CH3 1 2 4 1 2 3 4 (butane-1) (butene-2) GENERAL ORGANIC CHEMISTRY  MARKS 35 (c) Propanol (C3 H7 OH) H 3C  CH CH 3 H3 C C H2  C H2  O H | n-propyl alcohol OH iso-propyl alcohol (propanol-1) (propanol-2) FU N C T I ON A L I S OM E RI SM The compounds having the same molecular but different functional groups are said to exhibit functional isomerism. Such compounds are termed functional isomers. For example, (a) For C2H 6 O Ether Alcohol H 3C · O · CH3 H3 C · CH2 · OH (methoxymethane) dimethyl ether (ethanol) ethyl alcohol (b) The molecular formula C 3H6O represents two functional isomers. Aldehyde Ketone H3 C · CH 2 · CHO O (propionaldehude) propanal || H 3C · C · CH 3 (acetone) propanone (c) Carboxylic acids and esters CH 3CH 2 COOH CH3 COOCH3 Propanoic acid Methyl ethanoate Only Methanoic acid cannot have its isomeric ester. (d) Dienes, allenes and alkynes CH2 = CHăCH = CH 2 CH 2 = C = CHăCH 3 CH 3 CH2 C   CH Buta ă 1, 3 ă diene Buta ă 1, 2, ă diene But ă 1 ă yne (An allene) (e) Cyanides and Isocyanides RăCN R ăN C Alkyl cyanide Alkyl isocyanide (f) Nitro alkanes and alkyl nitrites O R N RăOăN =O O Alkyl niytites Nitroalkanes GENERAL ORGANIC CHEMISTRY  36 MARKS (g) 1Ĉ, 2Ĉ and 3Ĉ amines CH3 CH3 CH2 CH 2 NH 2 CH3 CH 2 NHCH3 | H3C  N  CH3 propan ă 1 ă amine N ă methyl ethanamine N, N ă Dimethyl methanamine (1Ĉ amine) (2Ĉ amine) (3Ĉ amine) (h) Aromatic alcohols, phenols and ethers CH2 OH OCH3 OH CH3 Benzyl Alcohol Anisole Oă(cresol) Met amerism This type of isomerism arises from the unequal distribution of carbon atoms on either side of the functional group in the molecule of compounds belonging to the same homologous series. For example, (a) diethyl ether and methylpropyl ether are metamers. H 5 C2ăOăC 2H 5 H3C ăOăC3 H7 (diethylether methylpropyl ether (eethoxyethane) (methoxypropane) (b) A k et on i c com p ou n d h av i n g t h e m ol ecu l ar f or m u l a C 5H 10O O O || || H 5C2  C  C2 H 5 H3 C C  C3 H7 diethyl ketone methyl propyl ketone (pentan-3-one) (pentan-2-one) T a u t om e r i s m It is a special type of functional isomerism in which an -hydrogen atom is shifted from one position (atom-1) to another (atom-3). This is referred as 1, 3-shift. Such shfits are common between a carbonyl compound containing an -hydrogen atom and its enol form. R' R' | | R 1 C  2 C  R''   R 1 C  2 C  R'' | 3|| | H O 3 Keto form OH Enol form GENERAL ORGANIC CHEMISTRY  MARKS 37 H = ( CăH + CăC + C=0) ă (C=C + CăO + OăH) = 359 ă 347 = 12 kcal/mol Thus, generally keto form is more stable than enol form by 12 kcal. So, in most cases, the equilibrium lies towards the left. Mostly the keto form is more stable than enol form but in certain cases, enol form can become the predominant form. The enol form is predominant in following cases : 1. Molecules in which the enolic double bond is in conjugation with another double bond/phenyl ring. In such cases, sometimes interamolecular hydrogen bonding also stabilizes the enol. R R C C R´ C C R´ H O O Keto form H Enol form (crossăconjujation) CH CH3 C CH2 C OEt CH3 C C OEt O O O O H Keto form Enol form (Crossăconjugation and intramolecular hydrogen bonding) CH CH3 C CH2 C CH3 CH3 C C CH3 O O O O H Keto form Enol form (Crossăconjugation and intramolecular hydrogen bonding) 2. Molecules, which contain two bulkyl aryl groups. Me Ar Ar C C H C C H where Ar = Me Ar Ar H O H O Me keto form (5%) Enol form (95%) In the keto form of 2,2ădimesitylenthanal, the ArăCăAr bond angle is 109Ĉ, whereby the bulky aryl groups experience greater steric repulsion. This steric repulsion eases off when the keto form transforms to enol form, where the ArăCăAr bond angle widens to 120Ĉ. GENERAL ORGANIC CHEMISTRY  38 MARKS 3. When the enol is aromatic stabilized. O OH H H Keto from Enol from The extent of enolization is also affected by the solvent, concentration and temperature. Thus, acetoacetic ester has an enol content of 0.4% in water and 19.8% in toluene. This is because water reduces the enol content by hydrogen bonding with the carbonyl group, making this group less available for intramolecular hydrogen bonding. The effectiveness of intramolecular hydrogen-bonding in stabilizing the enol, with respect to the keto form is seen on varying the solvent and particularly on transfer to a hydroxylic solvent with MeCOCH2COMe. Solvent % Enol Thus, the proportion of enol in the non-polar solvent (hexane) is Gas phase 92 the same as in the gas phase and higher than in the liquid itself, the latter acting as a polar auto-solvent. The proportion drops Hexane 92 again in the more polar MeCN and more dramatically in water. Liquid 76 What is happening is the increasing relative stabilization of the keto form by solvation, this being particularly marked in water MeCN 58 where intramolelcular hydrogen bonding of the keto formÊs C=O H2O 15 groups can now take place as an alternative to its enolization. Also, the enol content of pentană2,4ădione (CH3COCH 2COCH 3) is found to be 95% and 45% at 27.5Ĉ and 275.5ĈC respectively. When a strong base is added to a solution of a ketone with -hydrogen atom, both the enol and ketone form can lose a proton. The resulting anion is same in both the cases as they differ only in the placement of electrons. They are not tautomers but canonical forms. R R C C·R C C·R R R H O O H + ă + + +H ăH +H ăH ă O R R ă C C·R C C·R R R O {Canonical form} {Canonical form} GENERAL ORGANIC CHEMISTRY  MARKS 39 Me c h a n i s m : In basic medium O H O OH ă ă CH3 · C · CH2 CH3 · C · CH2 OH ă OH + CH3 ă C = CH2 CH3 · C = CH2 H 2O ă O In acidic medium + O H O·H + H CH3 · C · CH3 CH3 · C · CH2 H + ăH OH CH 3 · C = CH 2 Ot h e r t y p e s o f t a u t o m e r i s m (i) PhenolăKeto tautomerism O OH H H Cyclohedxadienone Phenol In this case, enol form is more stable than keto form because of the aromatic stabilization. GENERAL ORGANIC CHEMISTRY 40 MARKS (ii) NitrosoăOxime tautomerism : R R C N C N R R H O OH Nitroso form Oxime form This equilibrium lies far to the right and as a rule nitroso compounds are stable only when there is no -hydrogen atom. (iii) Nitro-Aci tautomerism Aliphatic nitro compounds are in equilibrium with the aci forms. R O R  O R O  C N C N C N R  R O R H O H OH Nitro form Aci form The nitro form is much more stable than the aci form because nitro group has resonance. Aci form of nitro compounds is also called nitronic acids. (iv) ImineăEnamine tautomerism/cyanideăeminine tautomerism: R R C C R C C R R R H N R NH R Imine form Enamine form Imine form predominates generally. Enamines are stable only when there is no hydrogen atom attached to nitrogen. R R C C C C R R H N.. N H O || Note : Keto-enol tautomerism occurs in those compounds in which  C  bond is attached through the carbon of CăH bond when C is saturated. GENERAL ORGANIC CHEMISTRY  MARKS 41 Ex a m p l e Which will not show tautomerism : O || (a) CH 3  C  H (b) O O CH3 O O | || || (c) H 3C  C  C H (d) CH 2  CH  C  H | CH 3 Solution : (b), (c) & (d) will not show tautomerism. O || In (b) & (d)  C is not attached to saturated carbon or we can say that the carbon attached to O || the  C  group is not sp3 hybridized. O || In (c),  C  is attached to carbon which does no have any hydrogen bonded to itself. Therefore tautomerism is not possible in this case. Ex a m p l e Which will have more enol : Write the order of increasing enol content. O O || || (1) CH 3  C  CH 2  C  O  CH 3.. O O || || (2) CH 3  C  CH 2  C  CH 3 O O (3) || || C· CH 2 · C· CH 3 GENERAL ORGANIC CHEMISTRY  42 MARKS Solution : (1) O H O (2) O H O CH3 · C · CH · C · O · CH3 CH3 · C · CH · C · CH3 OH O OH O CH3 · C = CH · C · O CH3 CH3 · C = CH · C · CH3 (enol form) (enol form) (3) O H O · C · CH · C · CH3 OH O · C = CH · C · CH3 (enol form).. Due to presence of lone pair in (1) on  OCH , power of carbon to wi