Advices For Studying Organic Chemistry

8.9A STRUCTURE AND REACTIONS OF METHYLENE

1. Methylene (:CH 2 ), the simplest carbene, can be prepared by the decomposition of
   diazomethane (CH 2 N 2 ).
   −CH 2 NN+ or lightheat CH 2 + NN
   Diazomethane Methylene Nitrogen


2. The structure of diazomethane is a resonance hybrid of three structures:

I II III

−CH 2 NN+ CH 2 NN+ − −CH 2 NN+

3. Methylene adds to the double bond of alkenes to form cyclopropanes:

CC C

C

C

H H

+ CH 2

Alkene Methylene Cyclopropane

8.9B

1. M are stereospecific.

REACTIONS OF OTHER CARBENES: DIHALOCARBENES

ost reactions of dihalocarbenes

CC

+ C in the product, they will b

CC

CCl 2

Theadditionof:CX 2 is stereospecific.

If the R groups of the alkene are trans

e trans in the

product. (If the R groups were initially

)

2.

from.

Cl Cl cis, they would be cis in the product

Dichlorocarbenes can be synthesized by the α elimination of hydrogen chloride

chloroform

RO −K+ + H CCl 3 RO Η+ − CCl 3 + K+ slow + Cl^ −
Dichlorocarbene

CCl 2