Nomenclature of Functional Groups PDF

NOMENCLATURE OF FUNCTIONAL GROUPS Alkanes The formal system of nomenclature used today is one proposed by the International Union of Pure and Applied Chemistry (IUPAC). Underlying the IUPAC system of nomenclature for organic compounds is a fundamental principle: Each different compound s...

NOMENCLATURE OF FUNCTIONAL GROUPS Alkanes The formal system of nomenclature used today is one proposed by the International Union of Pure and Applied Chemistry (IUPAC). Underlying the IUPAC system of nomenclature for organic compounds is a fundamental principle: Each different compound should have an unambiguous name. The IUPAC system for naming alkanes is not difficult to learn, and the principle involved are used in other families as well. The name of unbranched alkanes are; Number of Formula Number of Formula Name Name Carbons (n) (CnH2n+2) Carbons (n) (CnH2n+2) 1 Methane CH4 17 Heptadecane C17H36 2 Ethane C2H6 18 Octadecane C18H38 3 Propane C3H8 19 Nonadecane C19H40 4 Butane C4H10 20 Eicosane C20H42 5 Pentane C5H12 21 Henicosane C21H44 6 Hexane C6H14 22 Docosane C22H46 7 Heptane C7H16 23 Tricosane C23H48 8 Octane C8H18 30 Triacontane C30H62 9 Nonane C9H20 31 Hentriacontane C30H62 10 Decane C10H22 40 Tetracontane C40H82 11 Undecane C11H24 50 Pentacontane C50H102 12 Dodecane C12H26 60 Hexacontane C60H122 13 Tridecane C13H28 70 Heptacontane C70H142 14 Tetradecane C14H30 80 Octacontane C80H162 15 Pentadecane C15H32 90 Nonacontane C90H182 16 Hexadecane C16H34 100 Hectane C100H202 Page 1 of 11 Branched-Chain Alkanes 1. Locate the longest continuous chain of carbon atoms; this chain determines the parent name for the alkane. CH3CH2CH2CH2CHCH3 CH3CH2CH2CH2CHCH 3 CH2 CH3 CH3 2. Number the longest chain beginning with the end of the chain nearer the substituent. Substiuent 7 6 5 4 3 CH3CH2CH2CH2CHCH3 6 5 4 3 2 1 CH3CH2CH2CH2CHCH 3 2 CH2 Substiuent CH3 1 CH3 3. Use the numbers obtained by application of rule 2 to designate the location of the substituent group. 7 6 5 4 3 CH3CH2CH2CH2CHCH3 6 5 4 3 2 1 CH3CH2CH2CH2CHCH 3 2 CH2 CH3 1 CH3 2-Methylhexane 3-Methylheptane The parent name is placed last; the substituent group, preceded by the number indicating its location on the chain, is placed first. Page 2 of 11  4. When two or more substituents are present, give each substituent a number corresponding to its location on the longest chain. CH3CH CH2 CHCH 2CH3 CH3 CH2 CH3 4-Ethyl-2-methylhexane The substituent groups are listed alphabetically. In deciding on alphabetically order disregard multiplying prefixes such as “di” and “tri”. 5. When two substituents are present on the same carbon, use the number twice. CH3 CH3CH C CHCH 2CH3 CH2 CH3 3-Ethyl-3-methylhexane 6. When two or more substituents are identical, indicate this by the use of the prefixes di-, tri-, tetra-, and so on. CH3 CH3 CH3 CH3CCHCCH 3 CH3CH CHCH 3 CH3CHCHCHCH 3 CH3 CH3 CH3 CH3 CH3 CH3 2,3-Dimethylbutane 2,3,4-Trimethylpentane 2,2,4,4-Tetramethylpentane Page 3 of 11 7. When two chains of equal length compete for selection as the parent chain, choose the chain with the greater number of substituents. 7 6 5 4 3 2 1 CH3CH2 CH CH CH CH CH3 CH3 CH2 CH3 CH3 CH2 CH3 2,3,5-Trimethyl-4-propylheptane (four substituents) 8. When branching first occurs at an equal distance from either end of the longest chain, choose the name that gives the lower number at the first point of difference. 6 5 4 3 2 1 H3C CH CH2 CH CH CH3 CH3 CH3 CH3 2,3,5-Trimethylhexane (not 2,4,5-Trimethylhexane) Branched-Chain Alkyl Groups 1. Three-Carbon Groups CH3CH2CH2 Propyl group CH3CH2CH3 Propane H3C CH 1-Methylethyl or isopropyl group CH3 1-Methylethyl is the systematic name; isopropyl is a common name. Numbering always begins at the point where the group is attached to the main chain. Page 4 of 11  2. Four-Carbon Groups CH3CH2CH2CH2 Butyl group CH3CH2CH2CH3 Butane H3CH2C CH 1-Methylpropyl or sec-butyl group CH3 CH3CHCH 2 2-Methylpropyl or isobutyl group CH3 CH3CHCH 3 CH3 CH3 Isobutane CH3C 1,1-Dimethylethyl or tert-butyl group CH3 4 alkyl groups: 2 derived from butane; 2 derived from isobutane. CH3CH2CH2CHCH 2CH2CH3 H3C CH CH3 4-(1-Methylethyl)heptane or 4-isopropylheptane CH3CH2CH2CHCH 2CH2CH2CH3 H3C C CH3 CH3 4-(1,1-Dimethylethyl)octane or 4-tert-butyloctane The common names isopropyl, isobutyl, sec-butyl, tert-butyl are approved by the IUPAC for the unsubstituted groups. In deciding on alphabetically order disregard structure-defining prefixes that are written in italics and separated from the name by a hyphen. Thus “tert-butyl” precedes “ethyl”, but “ethyl” precedes “isobutyl”. Page 5 of 11  5. The common name neopentyl group is approved by the IUPAC. CH3 H3C C CH2 CH3 2,2-Dimethylpropyl or neopentyl group Cycloalkanes Cycloalkanes with only one ring are named by attaching the prefix cyclo- to the names of the alkanes possessing the same number of carbon atoms. Naming substituted Cycloalkanes is straightforward: We name them as alkylcycloalkanes, haloalkanes, alkylcycloalkanols, and so on. If only one substituent present, it is not necessary to designate its position. When two or more substituents are present, we number ring beginning with the substituent first in the alphabet and number in the direction that gives the next substituent the lower number possible. When three or more substituents are present, we begin at the substituent that leads to the lowest set of locants. 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 it is appropriate to name the compounds as cycloalkanes. Page 6 of 11  Alkenes and Cycloalkenes 1. Determine the parent name by selecting the longest chain that contains the double bond and change the ending of the name of the alkane of identical length from -ane to -ene. 2. Number the chain so as to include both carbon atoms of the double bond, and begin numbering at the end of the chain nearer the double bond. Designate the location of the double bond by using the number of the first atom of the double bond as a prefix. The locant for the alkene suffix may precede the parent name or be placed immediately before the suffix. 3. Indicate the locations of the substituent groups by the numbers of the carbon atoms to which they attached. 4. Number substituted cycloalkenes in the way that gives the carbon atoms of the double bond the 1 and 2 positions and that also gives the substituent groups the lower numbers at the first point of difference. 5. Name compounds containing a double bond and an alcohol group as alkenols (or cycloalkenols) and give the alcohol carbon the lower number. 6. Two frequently encountered alkenyl groups are the vinyl group and the allyl group. 7. If two identical groups are on the same side of the double bond, the compound can be designated cis; if they are on opposite sides it can be designated trans. Alkynes Alkynes are named in much the same way as alkenes. Unbranched alkynes, for example, are named by replacing the –ane of the name of the corresponding alkane with the ending –yne. The chain is numbered to give the carbon atoms of the triple bond the lower possible numbers. The lower number of the two carbon atoms of the triple bond is used to designate the location of the triple bond. The location of substituent groups of branched alkynes and substituted alkynes are also indicated with number. An –OH group has priority over the triple bond when numbering the chain of an alkynol. Page 7 of 11  Alkyl Halides or Haloalkanes Alkyl halides are compounds in which a halogen atom (fluorine, chlorine, bromine, or iodine) replaces a hydrogen atom of an alkane. Alkyl halides are also called haloalkanes. We simply name the alkyl halides is so straightforward that it is worth describing here. We simply name the alkyl group attached to the halogen and add the word fluoride, chloride, bromide, or iodide. Alcohols The characteristic functional group of this family is the hydroxyl (OH) group attached to an sp3 hybridized carbon atom. As with alkyl halides, alcohols are classified into three groups: primary (1°), secondary (2°), or tertiary (3°) alcohols. This classification is based on the degree of substitution of the carbon to which the hydroxyl group is directly attached. One way of naming alcohols is to name the alkyl group that is attached to the –OH and add the word alcohol. Ethers Ethers have the general formula R – O – R¢, where R¢ may be an alkyl or phenyl group different from R. Ethers can be thought of as dialkyl derivatives of water. One way of naming ethers is to name two alkyl groups attached to the oxygen atom in alphabetical order and add the word ether. If the two alkyl groups are the same, we use the prefix di-. Amines Just alcohols and ethers may be considered as organic derivatives of water, amines may be considered as organic derivatives of ammonia. One way of naming amines is to name in alphabetic order the alkyl groups attached to the nitrogen atom, using the prefixes di- and tri- if the groups are the same. Page 8 of 11  Aldehydes and Ketones Aldehydes and ketones both contain the carbonyl group –a group in which a carbon atom has a double bond to oxygen. The carbonyl group in aldehydes is bonded to at least one hydrogen atom, and in ketones it is bonded to two carbon atoms. One way of naming aldehydes is to name the alkyl group that is attached to the carbonyl group and add the suffix -al. One way of naming ketones is to name two alkyl groups attached to the carbonyl group in alphabetical order and add the word ketone. If the two alkyl groups are the same, we use the prefix di-. Carboxylic Acids, Esters, and Amides Carboxylic acids, esters, and amides all contain a carbonyl group that is bonded to an oxygen or nitrogen. Atom. Carboxylic acids have a hydroxyl group bonded to a carbonyl group. Esters have an alkoxyl group (– OR) bonded to a carbonyl group and are related to carboxylic acids by replacement of the hydroxyl group with the alkoxyl group. Amides have a nitrogen atom bonded to a carbonyl group and are related to acids and esters by replacement of their hydroxyl or alkoxyl group with a substituted or unsubstituted nitrogen atom. The IUPAC systematic or substitutive names for carboxylic acids are obtained by dropping the final –e of the name alkane corresponding to the longest chain in the acid and by adding –oic acid. The carboxyl carbon atom is assigned number 1. Esters The names of esters are derived from the names of the alcohol (with the ending –yl) and the acid (with the ending –ate or –oate). The portion of the name derived from the alcohol comes first. Page 9 of 11  Acyl Halides Acyl halides are also called acid halides. They are named by dropping the –ic acid from the name of the acid and then adding –yl chloride) Anhydrides Most anhydrides are named by dropping the word acid from the name of the carboxylic acid and then adding the word anhydride. Amides Amides that have no substituent on nitrogen are named by dropping –ic acid from the common name of the acid (or –oic acid from the substitutive name) and then adding –amide. Alkyl groups on the nitrogen atom of amides are named as substituents, and the named substituent is prefaced by N- or N,N-. Nitriles A nitriles has the formula R – C º N or R – CN. In IUPAC systematic nomenclature, acyclic nitriles are named by adding the suffix nitrile to the name of the corresponding hydrocarbon. The carbon atom of the – C º N group is assigned number 1. Priority of some functional groups. RCO2H > RCO2R¢ > RCOX > RCO2COR¢ > RCONR¢2 > RCºN > RCOH > RCOR > ROH > RNR¢2 > R2C = CR¢2 > RC º CR¢ > R > C6H5 > ROR¢ > X > RNO2 Carboxylic Acids > Esters > Acid Halides > Anhydrates > Amides > Nitriles > Aldehydes > Ketones > Alcohols > Amines > Alkenes > Alkynes > Alkyls > Phenyl > Halogens > Nitro Page 10 of 11  Table. Important Families of Organic Compounds Specific IUPAC Common General Functional Family Example Name Name Formula Group C–H and Alkane CH3CH3 Ethane Ethane RH C–C bond RCH=CH2 RCH=CHR Alkene CH2=CH2 Ethane Ethylene C C R2C=CHR R2C=CR2 HC≡CR Alkyne HC CH Ethyne Acetylene C C RC≡CR Aromatic Benzene Benzene ArH Aromatic ring Haloalkane CH3CH2Cl Chloroethane Ethyl chloride RX C X Alcohol CH3CH2OH Ethanol Ethyl alcohol ROH C OH Methoxy- Ether CH3OCH3 Dimethyl ether ROR C O C methane RNH2 Amine CH3NH2 Methanamine Methylamine R2NH C N R3 N O O O Aldehyde Ethanal Acetaldehyde CH3CH RCH C H O O O Ketone Propanone Acetone C C C CH3CCH3 RCR' Carboxylic O O O Ethanoic acid Acetic acid acid CH3COH RCOH C OH O O O Methyl Ester Methyl acetate C O C CH3COCH3 ethanoate RCOR' O CH3CONH2 O Amide Ethanamide Acetamide CH3CONHR’ CH3CNH2 CH3CONR’R” C N Nitrile H3CC N Ethanenitrile Acetonitrile RCN C N Page 11 of 11