Question

Multiple choice. Choose the best answer possible.

Which of the following is the correct order of decreasing acid strength (more acidic > less acidic)? a. CH3CH2OH> CICH2COOH > BrCH2COOH b. FCH2COOH > CH3COOH > F2CHCOOH oc. FCH2COOH > CH3COOH > CH3OH d. CH3COOH > CICH2COOH > CH3OH

Answer 1

Solution:

1)

Acidity depends on the stability of conjugate base.So,lets see the order of acidity for all molecules.

F2CHCOOH will be most stable as of its conjugate base CF2COO- will be most stable as due to resonance in carboxylic group between two oxygen atoms.Also, fluorine atom is electronegative atom which will stabilse this conjugate base with -Induction effect and it have 2 Fluorine atoms. So, its conjugate base will be most stable.Hence, Strongest the acid.

Then FCH2COOH will be more acidic as explained previously it has 1fluorine so,it will be less acidic than above molecule.

Then ClCH2COOH will be more acidic as explained previous due to resonance and as electronegativity of Chlorine is less than of fluorine. So, it will be less acidic than FCH2COOH

It will be followed by BrCH2COOH then CH3COOH

As electronegativity order, (F>Cl>Br>H).

Also, Remember carboxylic acid are more acidic than alcohols as of their conjugate base is more stable becuase there is resonance stabilized conjugate base but there is no as such resonance in alchol conjugate base.

So, All the carboxylic acid will be more stable than alcohols. CH3OH will be more acidic than CH3CH2OH because conjugate base of CH3OH is more stable as less +Inductive effect of alkyl chain than in CH3CH2OH.

So, Correct order of acidity will be

F2CHCOOH > FCH2COOH > ClCH2COOH > BrCH2COOH> CH3COOH > CH3OH > CH3CH2OH

so, correct ans will by seeing the order

(c) F2CH2COOH > CH3COOH > CH3OH.

(a), (b), (d) won't be possible as doesn't match with above acidity order.

(2) As recomment by IUPAC,

Ph is phenyl with 1more carbon it is called benz group.

-C $\large \equiv$ N is nitrile group.

-CONH2  is amide group.

-COOH is carboxylic acid group.

So,compund first is benzonitrile as it contains Ph and CN group, second is benzamide as it contains Ph and CONH2 while third is benzoic acid as it contains Ph and COOH group.

So, correct option is (a)

(b), (c) and (d) not possible.

Hope, it helps. :)