Organic Chemistry Principles In Context: A Story Telling Historical Approach by Green Mark M

Author:Green, Mark M [Green, Mark M]
Language: eng
Format: epub
Publisher: ScienceFromAway, New York
Published: 2012-10-08T21:00:00+00:00

FIGURE 6.20

Source of the Electron Withdrawing Characteristics of Three Substituents on Benzene: Nitro, Trichloromethyl and Carboxyl

The consequence of an electron deficient group bonded to a carbon atom on the benzene ring means that substitution of the newly incoming electrophile (NO2+ in Figure 6.19) at the ortho or para position in placing a positive charge at that carbon atom will be an unfavorable situation.

On the contrary, the consequence of an electron rich group bonded to a carbon atom on the benzene ring, which can stabilize an adjacent carbocation, means that substitution of the newly incoming electrophile at the ortho or para position in placing a positive charge at that carbon atom will be a favorable situation.

Therefore, reactions 1 and 3 favor ortho-para substitution while reactions 2, 4 and 5 disfavor ortho and para substitution and in disfavoring these ortho, para sites, meta substitution, although occurring slowly, nevertheless dominates the product distribution. In reaction 2 we see 93% of the substitution product is meta, in reaction 4, 64% is meta substitution, and in reaction 5, 80% is meta substitution. We’ll leave for later more advanced inquiries in organic chemistry to delve into the details of the differing proportions of meta substitution for these reactions.

The difference in the ortho para ratio in 1 and 3 has a reasonable answer you will be given the opportunity to come up with in addressing problem 6.50 with the help of problem 6.51.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.