Question

Q3V (15 Marla) Explain the following: 1. Alkene stability, 2. Ierin structural J. Molecular Orbitals of Carbon Carbon 4. Inductive Effects

Answer 1

1. Alkenes stability. Alkenes are hydrocarbon chains that have at least one-one carbon-carbon double bond Stability of alkenes increases with increase in substitution. Since some bonds are formed and break in every hydrogenation reaction. The heat of hydrogenation measure the stability of alkenes. Lower the heat of hydrogenation higher the stability of alkenes. Internal alkenes are more stable than terminal alkenes because they are connected to more carbons on the chain whereas terminal alkenes are located at the end of the chain; the double bond is only connected to one carbon called primary. Primary carbon are least stable 2. Isomerism structural: A structural isomer is a type of isomer in which molecules have same molecular formula but different bonding patterns and atomic organization as opposite to stereo-isomers in which molecular bonds are always same order and only spatial arrangements differs. There are three types of structural isomers that are positional isomers, functional isomers and chain isomers. Chain isomers have same formula but different arrangement or branches. Functional isomers have same formula but different functional groups.

3. Molecular orbital of Carbon-Carbon: Two Carbon atoms combine by sigma bond overlapping with two sp2 orbital. Each carbon atom forms two covalent bonds with hydrogen by s-sp2 overlap all with 120 degree angle. The carbon- carbon bond is covalent bond. The most common bond is single bond which is formed by two electrons one from each atom. It also forms double bonds in alkenes and triples bonds in alkynes. 4. Inductive effect: The polarization of sigma bond due to electron withdrawing or electron donating effect of adjacent groups or atoms is called inductive effect. Stability is directly proportional to inductive effect. As Inductive effect of alkyl group decreases its stability decreases. More the number of alkyl groups on carbon atom carrying the positive charge, greater would be the dispersal of the charge and more stable would be the carbon cation.