What are alkenes ?
in their molecules. The alkenes are also called olefins because the lower gaseous members from oily products with chlorine or bromine. The double bond in an alkene is also known as an Ethylenic double bond or Olefinic bond. The general formula of alkene is CnH2n where n = 2,3, 4...... etc. Since there can be no alkene having one carbon (due to the absence of >C = C< double bond), the first member of the series in bond), the first member of the series is C2H4. It is commonly known as ethylene.
What are the necessary and sufficient conditions for a compound to exhibit geometrical isomerism ?
Conditions for geometrical isomerism: There are two necessary conditions for a compound to possess geometrical isomerism:
(i) It must contain a carbon-carbon double bond in the molecule.
(ii) Two unlike atoms or groups must be linked to each doubly bonded carbon atoms.
Geometrical isomerism among alkenes does not occur when the doubly bonded carbon carry identical atoms or groups. For example, AAC = CAB does not exhibit geometrical isomerism.
What kind of structural isomerism is shown by alkenes ?
Alkenes show two types of structural isomerism:
(i) Chain isomerism: It is caused by different arrangements of carbons in the chain. For example.
(ii) Position isomerism: It is caused due to the different positions of a double bond in the alkene. For example 1-butene and 2-butene.
Can eclipsed and staggered conformations of ethane be isolated? Give reasons.
No, because the difference of energy between these two conformations is very small, so even at room temperature these two interconvert rapidly and hence cannot be isolated.
Switch
bonds in the following structures:
bonds 2
bonds 4
bonds 1
