Question

Discuss the importance of solvent and temperature control in organic synthesis.

Answer 1

Organic synthesis mainly involve three types of reaction

1. Nucleophilic Substitution reaction : Here one group or atom is substituted by other group and atom (called nucleophile)

A-L + Nu A-Nu + L

For a substitution reaction, the polarity is very important .

In a SN1 reaction most of cases favoured by polar protic solvent like water, alcohol etc where solvent can stabilize the intermediate carbocation whereas SN2 reaction is favoured by polar aprotic solvent like DMF, DMSO which can increase the strength of nucleophile.

2. Elemination reaction: Here, two substituents are removed from a molecule in either a one or two-step mechanism. The one-step mechanism is known as the E2 reaction, and the two-step mechanism is known as the E1 reaction.

Higher temerature always favours elemination reaction over substitution reaction.

Increasing temperature results in a gradual increase in elimination products relative to substitution. That’s because temperature is gradually leading to an increase in the rate constant for elimination versus rate constant for substitution.

3. Addition reaction: Here addition of two groups take place across double bond of an alkene. This type of reaction is exothermic and hence will be favoured in low temperature.

A=B + X2    X-A-B-X