Chapter 3

CHAPTER 3 ALKENES & ALKYNES

Structure and Nomenclature General

formula for alkene, CnH2n and alkyne, CnH2n-2 IUPAC nomenclature: nomenclature alkenes and alkynes are named like alkanes but the ending is changed from “ane” to “ene” or “yne”.

Nomenclature of alkenes

Diene Triene

- 2 double bonds

– 3 double bonds Tetraene – 4 double bonds

Alkyl

attached to the alkene chain – the lowest numbering is still given to alkene chain.

Alkenes

as substituents

Exercise

ALKYNES: Nomenclature

Naming

Compounds with Both Double and Triple Bond

Exercise:

Skeletal, Positional and Functional Isomerism in alkenes and alkynes Skeletal isomers – differ in the arrangement of carbon atoms Positional isomers – vary in the position of an atom or group other than carbon or in the position of a carbon-carbon double or triple bond. Functional isomers – exhibit structural variations that place them in different classes of organic compound

Example:

C4H8 Positional isomer = 1-butene & 2-butene

Skeletal isomer = 2-methylpropene

Functional isomers = cyclobutane & methylcyclopropane

EXERCISE:draw

and name the possible isomers of the C5H8 . Identify the positional and skeletal isomers.

Functional Isomerism in Organic Chemistry Functional isomers belongs to different classes of organic compounds because the posses different functional group.  Major organic functional groups are shown below: 



Example: alcohol (R—OH) and ether (R—O—R’), C3H8O

CH3CH2CH2OH and CH3OC2H5 an alcohol

an ether

Alkene (C=C) and cycloalkane C4H8 CH3CH2CH=CH2

and

Exercise:

C5H10O

GEOMETRIC ISOMERISM IN ALKENES A) Cis-Trans Isomerism

B) The E-Z System

Units of Unsaturation in Hydrocarbon (Double bonds equivalent)