Advices For Studying Organic Chemistry

3. Ketones can be converted to gem-dichloride through their reaction with
   phosphorus pentachloride which can be used to synthesize alkynes.

C CH

3

O

PCl 5

0 oC

C

1.3 NaNH 2

2. H+
   Cyclohexyl methyl
   ketone

A gem-dichloride

(70-80%)

Cyclohexylene

(46%)

mineral oil

heat

(−POCl 3 )

C CH

3

Cl

Cl

CH

7.11 THE ACIDITY OF TERMINAL ALKYNES

1. The hydrogen atoms of ethyne are considerably more acidic than those of ethane
   or ethane:

HCCH CC

H

H

H

H

HCCH

HH

HH

pKa = 25 pKa = 44 pKa = 5^0

1) The order of basicities of anions is opposite that of the relative acidities of the

hydrocarbons.

Relative Basicity of ethanide, ethenide, and ethynide ions:

CH 3 CH 2 :– > CH 2 =CH:– > HC≡C:–

Relative Acidity of hydrogen compounds of the first-row elements of the periodic

table:

H–OH > H–OR > H–C≡CR > H–NH 2 > H–CH=CH 2 > H–CH 2 CH 3

Relative Basicity of hydrogen compounds of the first-row elements of the periodic

table:

-^
:OH < –:OR < –:C≡CR < –:NH 2 < –:CH=CH 2 < –:CH 2 CH 3