trans form non-polar. (ii) CH = CBr (iii) C H CH = CH – CH (iv) CH CH = CCl CH (iii) and (iv). In structures (i) and (ii), two identical groups are attached to one of the doubly bonded carbon atom. .
. Preparation . From alkynes: Alkynes on partial reduction with calculated amount of dihydrogen in the presence of palladised charcoal partially deactivated with poisons like sulphur compounds or quinoline give alkenes. Partially deactivated palladised charcoal is known as Lindlar’s catalyst .
Alkenes thus obtained are having cis geometry. However, alkynes on reduction with sodium in liquid ammonia form trans alkenes. ( . ) ( .
) iii) CH ≡ CH+H Pd/C CH =CH ( . ) Ethyne Ethene iv) CH –C ≡ CH+H Pd/C CH –CH =CH Propyne Propene ( . ) Will propene thus obtained show geometrical isomerism? Think for the reason in support of your answer.
. From alkyl halides : Alkyl halides (R-X) on heating with alcoholic potash (potassium hydroxide dissolved in alcohol, say, In the case of solids, it is observed that the trans isomer has higher melting point than the cis form. Geometrical or cis-trans isomerism is also shown by alkenes of the types XYC = CXZ and XYC = CZW Problem . Draw cis and trans isomers of the following compounds.
Also write their IUPAC names : (i) CHCl = CHCl (ii) C H CCH = CCH C H Problem . Which of the following compounds will show cis-trans isomerism? (i) (CH ) C = CH – C H cis -But- -ene ( µ = .33D) trans -But- -ene ( µ = ) ethanol) eliminate one molecule of halogen acid to form alkenes. This reaction is known as dehydrohalogenation i.e., removal of halogen acid.
This is example of β -elimination reaction , since hydrogen atom is eliminated from the β carbon atom (carbon atom next to the carbon to which halogen is attached). ( . ) Na ture of halogen atom and the alkyl group determine rate of the