Organic Chemistry Lecture Notes PDF

ORGANIC CHEMISTRY 1. Introduction to Alkanes & Cycloalkanes  Alkanes and cycloalkanes are hydrocarbons in which all the carbon-carbon (C–C) bonds are single bonds  Hydrocarbons that contain C═C: Alkenes Hydrocarbons that contain C≡C: Alkynes  Alkanes: CnH2n+2...

ORGANIC CHEMISTRY 1. Introduction to Alkanes & Cycloalkanes  Alkanes and cycloalkanes are hydrocarbons in which all the carbon-carbon (C–C) bonds are single bonds  Hydrocarbons that contain C═C: Alkenes Hydrocarbons that contain C≡C: Alkynes  Alkanes: CnH2n+2 5 3 1 e.g. 6 4 2 hexane (C6H14)  Cycloalkanes: CnH2n e.g. cyclohexane (C6H12) 1A. Sources of Alkanes: Petroleum  Petroleum is the primary source of alkanes.  It is a complex mixture of mostly alkanes and aromatic hydrocarbons with small amounts of oxygen-, nitrogen-, and sulfur- containing compounds  Petroleum refining Distillation is the first step in refining petroleum. Its components are separated based on different volatility More than 500 different compounds are contained in petroleum distillates boiling below 200oC  Petroleum refining (Cont’d) The fractions taken contain a mixture of alkanes of similar boiling points Mixture of alkanes can be used as fuels, solvents, and lubricants  Gasoline The demand of gasoline is much greater than that supplied by the gasoline fraction of petroleum Converting hydrocarbons from other fractions of petroleum into gasoline by “catalytic of alkanes catalysts highly branched cracking” mixture o (C12 and higher) ~ 500 C hydrocarbons (C5 - C10)  Typical Fractions Obtained by Distillation of Petroleum Boiling Range # of Carbon Use of Fraction (oC) Atoms per Molecule Below 20 C1 – C 4 Natural gas, bottled gas, petrochemicals 20 – 60 C5 – C 6 Petroleum ether, solvents 60 – 100 C6 – C 7 Ligroin, solvents 40 – 200 C5 – C10 Gasoline (straight-run gasoline)  Typical Fractions Obtained by Distillation of Petroleum (Cont’d) Boiling Range # of Carbon Use of Fraction (oC) Atoms per Molecule 250 – 400 C12 and higher Gas oil, fuel oil, and diesel oil Nonvolatile C20 and higher Refined mineral liquids oil, lubricating oil, and grease Nonvolatile solids C20 and higher Paraffin wax, asphalt, and tar 2. Shapes of Alkanes  All carbon atoms in alkanes and cycloalkanes are sp3 hybridized, and they all have a tetrahedral geometry  Even “straight-chain” alkanes are not straight. They have a zigzag geometry  “Straight-chain” (unbranched) alkanes Butane Pentane CH3CH2CH2CH3 CH3CH2CH2CH2CH3 Straight-chain alkanes: Alkanes with C’s connected to no more than 2 other C’s Also called normal alkanes  Branched-chain alkanes Isobutane Neopentane CH3 CH3 CH CH3 CH3 C CH3 CH3 CH3 Branched-chain alkanes: Alkanes with one or more carbon atoms connected to 3 or 4  Butane and isobutane have the same molecular formula (C4H10) but different bond connectivities.  Such compounds are called constitutional isomers Butane Isobutane  C4 and higher alkanes exist as constitutional isomers. The number of constitutional isomers increases rapidly with the carbon number Molecula # of Possible Molecula # of Possible r Const. r Const. Isomers Formula Isomers Formula C4H10 2 C9H20 35 C5H12 3 C10H22 75 C6H14 5 C20H42 366,319 C7H16 9 C40H82 62,481,801,147,3 41  Constitutional isomers usually have different physical properties Hexane Isomers (C6H14) Formula M.P. B.P. Density Refractive (oC) (oC) (g/mL) Index -95 68.7 0.6594 1.3748 -153.7 60.3 0.6532 1.3714 -118 63.3 0.6643 1.3765 -128.8 58 0.6616 1.3750 -98 49.7 0.6492 1.3688 3. IUPAC Nomenclature of Alkanes, Alkyl Halides, & Alcohols  One of the most commonly used nomenclature systems that we use today is based on the system and rules developed by the International Union of Pure and Applied Chemistry (IUPAC)  Fundamental Principle: Each different compound shall have a unique name Naming Alkanes  International Union of Pure and Applied Chemistry (IUPAC) system of nomenclature  The ending for all the names of alkanes is –ane  The names of most alkanes stem from Greek and Latin one two three four five meth- eth- prop- but- pent-  Unbranched alkanes Name Structure Name Structure Methan CH4 Hexane CH3(CH2)4CH e 3 Ethane CH3CH3 Heptan CH3(CH2)5CH e 3 Propane CH3CH2CH3 Octane CH3(CH2)6CH 3 Butane CH3CH2CH2CH3 Nonane CH3(CH2)7CH 3 Pentane CH3(CH2)3CH3 Decane CH3(CH2)8CH  Alkyl group (Cont’d) For an unbranched alkane, the hydrogen atom that is removed is a terminal hydrogen atom CH3 H CH3CH2 H CH3CH2CH2 H Methane Ethane Propane CH3 CH3CH2 CH3CH2CH2 Methyl Ethyl Propyl (Me) (Et) (Pr) 3B. Nomenclature of Branched-Chain Alkanes  Rule 1. Use the longest continuous carbon chain as parent name 7 6 5 4 3 6 5 4 3 2 1 CH3CH2CH2CH2CHCH3 CH3CH2CH2CH2CHCH3 2CH2 CH2 NOT 1CH3 CH3 (3-Methylheptane) (2-Ethylhexane)  Rule (Cont’d) 2. Use the lowest number of the substituent 3. Use the number obtained by Rule 2 to designate the location of the substituent 7 6 5 4 3 1 2 3 4 5 CH3CH2CH2CH2CHCH3 CH3CH2CH2CH2CHCH3 2CH2 6CH2 NOT 1CH3 7CH3 (3-Methylheptane) (5-Methylheptane)  Rule (Cont’d) 4. For two or more substituents, use the lowest possible individual numbers of the parent chain The substitutents should be listed alphabetically. In deciding alphabetical order, disregard multiplying prefix, such as “di”, “tri” etc.  Rule (Cont’d) 2 4 6 8 1 3 5 7 (6-Ethyl-2-methyloctane) NOT NOT 7 5 3 1 2 4 6 8 8 6 4 2 1 3 5 7 (3-Ethyl-7-methyloctane) (2-Methyl-6-ethyloctane)  Rule (Cont’d) 5. When two substituents are present on the same carbon, use that number twice 2 4 6 8 1 3 5 7 (4-Ethyl-4-methyloctane)  Rule (Cont’d) 6. For identical substituents, use prefixes di-, tri-, tetra- and so 5 on3 1 6 4 2 7 5 3 1 6 4 2 (2,4-Dimethylhexane) (2,4,5-Trimethylheptane) NOT NOT 2 4 6 1 3 5 1 3 5 7 2 4 6 (3,5-Dimethylhexane) (3,4,6-Trimethylheptane)  Rule (Cont’d) 7. When two chains of equal length compete for selection as parent chain, choose the chain with the greater number of substituents 7 1 1 6 4 2 4 2 5 3 3 5 NOT 6 7 (2,3,5-Trimethyl- (only three substituents) 4-propylheptane)  Rule (Cont’d) 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 1 NOT 5 3 1 2 4 6 4 2 3 5 (2,3,5-Trimethylhexane) (2,4,5-Trimethylhexane)  Example 1 Find the longest chain as parent 4 2 4 6 3 1 5 7 or 5 7 3 1 6 2  Example 1 (Cont’d) Use the lowest numbering for substituents 4 6 4 2 5 7 3 1 instead of 3 1 5 7 2 6 Substituents: two methyl groups 4 6 5 7  dimethyl 3 1 2  Example 1 (Cont’d) Complete name 4 6 5 7 3 1 2 (3,4-Dimethylheptane)  Example 2 5. Nomenclature of Alkenes & Cycloalkenes  Rule 1. Select the longest chain that contains C=C as the parent name and change the name ending of the alkane of identical length from –ane to –ene  Rule 2. Number the chain so as to include both carbon atoms of C=C, and begin numbering at the end of the chain nearer C=C. 3. Assign the location of C=C by using the number of the first atom of C=C as the prefix. 4. The locant for the alkene suffix may precede the parent name or be placed  Examples 1 2 3 4 CH2 CHCH2CH3 1-Butene (not 2-Butene) 1 2 3 4 5 6 CH3CH CHCH2CH2CH3 2-Hexene (not 3-Hexene)  Rule 3. Indicate the locations of the substituent groups by the numbers of the carbon atoms to which they are attached Examples 4 3 2 1 2-Methyl-2-butene (not 3-Methyl-2-butene)  Examples (Cont’d) 4 6 3 5 2 1 2,5-Dimethyl-2-hexene 3 1 NOT 4 2 5 6 2,5-Dimethyl-4-hexene  Rule 4. Number substituted cycloalkenes in the way that gives the carbon atoms of C=C the 1 and 2 positions and that also gives the substituent groups the lower numbers at the first point of difference  Example 1 6 2 5 3 4 3,5-Dimethylcyclohexene 2 NOT 3 1 4 6 5 4,6-Dimethylcyclohexene  Rule 5. Name compounds containing a C=C and an alcohol group as alkenols (or cycloalkenols) and give the alcohol carbon the lower number Examples OH 6 1 2 5 3 4 2-Methyl-2-cyclohexen-1-ol (or 2-Methylcyclohex-2-en-1-ol)  Examples (Cont’d) OH 4 2 5 3 1 4-Methyl-3-penten-2-ol (or 4-Methylpent-3-en-2-ol)  Rule 6. Vinyl group & allyl group Vinyl group Allyl group ethenyl OH 6 1 2 5 3 Ethenylcyclopropane 4 (or Vinylcyclopropane) (3-Allylcyclohexanol)  Rule 7. Cis vs. Trans Cis: two identical or substantial groups on the same side of C=C Trans: two identical or substantial groups on the opposite side of C=C Cl Cl Cl Cl cis-1,2-Dichloroethene trans-1,2-Dichloroethene  Example  Example (Cont’d) 6 (a) (b) 5 7 6 4 2 4 2 3 1 5 3 1 (c) (d) 6 2 4 2 4 6 7 5 3 1 1 3 5 7  Example (Cont’d) Complete name 2 4 6 1 3 5 7 4-tert-Butyl-2-methyl-1-heptene  Alkenes that have more than one double bond are named as dienes (2 – double bond), trienes (3 – double bonds) etc... 1,2 - Pentadiene 1,2,6 - Octatriene 6. Nomenclature of Alkynes  Alkynes are named in much the same way as alkenes, but ending name with –yne instead of –ene  Examples 3 2 2 3 6 4 1 Br 1 7 5 4 2-Heptyne 4-Bromo-1-butyne  Examples (Cont’d) 3 4 I Br 2 5 6 7 8 9 1 10 9-Bromo-7-iodo-6-isopropyl-8-methyl-3-decyne  OH group has priority over C≡C 4 3 1 2 2 3 OH NOT OH 1 4 3-Butyn-1-ol OH 5 6 7 OH 4 3 2 2 4 7 5 1 3 8 8 6 1 2-Methyl-5-octyn-2-ol NOT  If a compound contains both double bond and triple bonds then use both name ending :-enyne.  Give the lowest possible numbering to which ever comes first.  A double bond takes preference in numbering when the two are equidistant.  5-Nonen-2-yne Hexen-3-yne 2-hexen-5-yne 7. Physical Properties of Alkanes & Cycloalkanes  Boiling points & melting points  Boiling Point C6H14 Isomer (oC) 68.7 63.3 60.3 58 49.7 Physical Constants of Cycloalkanes # of C mp Densit Refractiv Atoms Name bp (oC) (oC) y e Index 3 Cyclopropane -33 -126.6 - - 4 Cyclobutane 13 -90 - 1.4260 5 Cyclopentane 49 -94 0.751 1.4064 6 Cyclohexane 81 6.5 0.779 1.4266 7 Cycloheptane 118.5 -12 0.811 1.4449 8 Cyclooctane 149 13.5 0.834 -