Nomenclature of Alkenes

Nomenclature of Alkenes Figure 10.1 Naming an alkene in which the longest carbon chain does not contain both atoms of the double bond

Cis-Trans (Z-E) Isomerism in Alkenes If each end of the double bond is attached to two different groups, then the compound exists in two different forms called (Diastereomers; These are non mirror image stereoisomers). If the two groups are identical we distinguish the two isomers by adding the prefix cis (same side) or trans (opposite sides) Example

If the groups attached to the double bond are different, we distinguish the two isomers by adding the prefix Z (same side) or E (opposite sides) depending on the atomic number of the atoms attached to each end of the double bond

Isomers and common names of simple alkenes

Ease of formation of alkenes: Saytzeff orientation: In dehydrohalogenation the preferred product is the alkene that has the greater number of alkyl groups attached to the doubly bonded carbon atoms (the more substituted alkene will form) Ease of formation of alkenes: R2C=CR2 > R2C=CHR > R2C=CH2, RCH=CHR > RCH=CH2 > CH2=CH2 Stability of alkenes: CH3CH2CHCH3 + KOH(alc)  CH3CH2CH=CH2 RCH=CH2 Br 1-butene 19% sec-butyl bromide + CH3CH=CHCH3 RCH=CHR 2-butene 81%

Mechanism dehydrohalogenation of alkyl halides (E2) one step , nonrearrangment

Mechanism of Dehydration (E1) two step carbocation form, rearrangment

Dehydration (Rearrangement)