Alkenes and Alkynes

Fundamentals of alkenes General methods of preparation of alkenes Physical Properties of alkenes Addition reactions of alkenes Ozonolysis of alkenes Oxidation of alkenes Miscellaneous Reactions of alkenes Dienes or Diolefins or Alkadienes Fundamentals of alkynes or acetylenes Methods of Preparation of alkynes Physical properties of alkynes Chemical Nature of alkynes Addition reactions of alkynes Oxidation of alkynes Miscellaneous reactions shown by alkynes Test for Unsaturation

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(viii)    Alkenyl groups : Residual part left after the removal of one H atom from alkene is known as alkenyl group. According to IUPAC nomenclature, these groups are named by replacing terminal 'e' of alkene by 'yl' e.g.

Group	Trivial name	IUPAC name
2        1 CH2=CH-	vinyl	ethenyl
3        2       1 CH2=CH-CH2-	allyl	prop-2-enyl
1    2       3 -CH=CH-CH3	-	prop-1-enyl
1       2     3      4 -CH2-CH=CH-CH3	crotyl	but-2-enyl

     The numbering in alkenyl group is started from the carbon with free valencies.

(ix)      Isomerism in alkenes : Alkenes show following isomerisms

            (i)         C₃H₆ : CH₃CH=CH₂       &         CH₂-CH₂     Ring chain isomerism

                                                                       CH₂

                                                                Cyclopropane

 

            (ii)        C₄H₈   (a)      CH₃CH₂CH=CH₂     but-1-ene

                                 (b)      CH₃CH=CH-CH₃     but-2-ene

                                 

(a)  and (b) show position isomerism

(a) and (c) show chain isomerism

(a) and (d) show ring-chain isomerism

(b) also shows Geometrical isomerism

                       

The number of isomers increase with increase in carbon atoms more rapidly than corresponding alkanes. (pentane has only 3 isomers)