Question

Define a) Inductive effect b)Hyperconjugation effect.

Answer 1

Hint: A reaction may or may not occur depending on the electron density at the site of reaction in the substrate. Inductive effect is one of the factors which influence the electron density.

Complete answer:
a) Inductive effect: It refers to the polarity produced in a molecule as a result of higher electronegativity of one atom compared to another. It involves sigma electrons. The sigma electrons are seldom shared equally between two atoms. This is due to the difference in electronegativity of atoms. Thus electrons shift towards a more electronegative atom which results in a certain degree of polarity. The more electronegative atom acquires small negative charge while less electronegative atom acquires small positive charge. It is divided into two groups a) \[ + I\] and b) $ - I$ effect. To differentiate between these two, carbon-hydrogen bonds are chosen as standard and zero effect is assumed. Atoms or groups which donate electrons towards a carbon atom are said to have \[ + I\] effect while atoms or groups which draw electrons away from a carbon atom are said to have $ - I$ effect.
b) Hyperconjugation effect: complete transfer of C-H sigma bond towards pi bond or positive charge or free electron is called H-effect (permanent effect). It is also called no-bond resonance and is given by Nathen and Baker. Condition of H- effect: 1) C-H sigma bond and positive charge should be in conjugation. Carbon which is attached to positively charged carbon is called $\alpha - C$ and H which is attached to $\alpha - C$ is called $\alpha - H$. So, if the number of $\alpha - H$ is more then there will be more number of hyperconjugation structures and more is the stability.
 2)If C-H sigma bond and free electrons/pi bond are in conjugation then there will be an H-effect.

Note:Inductive effect is not confined to the polarization of one bond. It is transmitted along a chain of carbon atoms and resonance effects are more important than hyperconjugation.