McMurry (Kap. 15,4) - substituents effect on acidity (carboxylic acid)

Question 1

There are a lot of difference between the Ka values of different carboxylic acids.

Trifluroacetic acid is 33 times as strong as acetic acid, why?

Answer 1

Any factor that stabilizes the carboxylate anion (baseform af carboxylsyren) will drive the equilibrium towards increased dissociation and thereby increased acidity.

Question 2

The electron withdrawing inductive effect of fluro atoms delocalize the negative charge in the trifluro acetate ion and thereby stabilizing the ion and increasing acidity in the CF3CO2H.

Answer 2

True.

Question 3

The more electron withdrawing substituents on a molecule, on an acetate ion, the more stable it will become, and the more acidic the corresponding acid form will be?

Answer 3

True.

And electron withdrawing groups will have the opposite effect (see table 15,3) - the substituents that are deactivating = stronger acid or activating = weaker acid.

Question 4

Can the substituents effect on the carboxylic acid be compared to the substituents effect on the aromatic ring and its effect on reactivity.

Answer 4

Yes, electron donating groups are activated towards further electrophillic substitution.

Aromatic ring with electron withdrawing group is deactivating.

Question 5

Because it is much easier to measure the acidity of substituted benzoic acid , then it is to measure the relative reactivity of an aromatic ring towards electrophillic substitution, the correlation between the two is useful when predecting reactivity.

find the acidity of the substituent and compare it with benzoic acid (substituent that strenghtens the acid - deactivating group - e withdrawing. Substituents that weakens the acid - e donating.

electron donating groups are activated towards further electrophillic substitution.

Aromatic ring with electron withdrawing group is deactivating.

Answer 5

yes