Advices For Studying Organic Chemistry

3. ium ions II or III at the carbon of each that bears
   the greater positive charge, in accord with Markovnikov regiochemistry.


4. The C–Br bond lengths of bromonium ions I, II, and III:

Nucleophile reacts with bromon

Fig al

stabilize the positive charge. A lesser electron density contribution

from bromine is needed because additional alkyl groups help stabilize

1) In the bromonium ion of ethene (I), the C–Br bond lengths are identical (2.06Å).

2)

ereas the one with the 1°carbon is 2.03Å.

lectron density from the bromine to the 2° carbon, because the

an the 1° carbon.

3 n

c

i) cates that significantly less

etter than the 1° carbon.

5.

2-methylpropene:

1) should focus on are those opposite the

three membered ring portion of the bromonium ion.

ure 8.B The carbon-bromine bond length (shown in angstroms) at the centr

carbon increases as less electron density from the bromine is needed to

the charge

In the bromonium ion of propene (II), the C–Br bond involving the 2° carbon is

2.17Å, wh

i) The longer bond length to the 2° carbon is consistent with the lesser

contribution of e

2° carbon can accommodate the charge better th

) I the bromonium ion of 2-methylpropene (III), the C–Br bond involving the 3°

arbon is 2.39Å, whereas the one with the 1°carbon is 1.99Å.

The longer bond length to the 3° carbon indi

contribution of electron density from the bromine to the 3° carbon, because the

3° carbon can accommodate the charge b

ii) The bond at the 1° carbon is like that expected for typical alkyl bromide.

The lowest unoccupied molecular orbital (LUMO) of ethane, propene, and

The lobes of the LUMO on which we