Advices For Studying Organic Chemistry

A

CH 3 CCHCH 2

CH 3

CH 3 CCHCH 2

CH 3

CH 3 CCHCH 2

CH 3

δ+ δ+

abcd

++

(^67)
ii) Structure 6 makes greater contribution means that the partial positive charge on
carbon b of the hybrid will be larger than the partial positive charge on carbon
d.
iii) It also means that the bond between carbon atoms c and d will be more like a
double bond than the bond between carbon atoms b and c.

13.5B ESTIMATING THE RELATIVE STABILITY OF RESONANCE

STRUCTURES

1. The more covalent bonds a structure has, the more stable it is.

This is structure is the most
stable because it contains
more covalent bonds.

CH +

2 CH CH CH^2

CH+

CH 2 CH CH CH 2 2 CH CH CH 2

89

−

10

−

2. Structures in which all of the atoms have a complete valence shell of electrons
   are especially stable and make large contributions to the hybrid.

1. Structure 12 makes a larger stabilizing contribution to the cation below than 11
   because all of the atoms of 12 have a complete valence shell.
   i) 12 has more covalent bonds than 11.

H 2 C+ O CH 3 H 2 C O+ CH 3

This carbon atom has

only six electrons.

The carbon atom has

eight electrons.

11 12

3. Charge separation decreases stability.
   
   
   1. Separating opposite charges requires energy.