Markovnikov's rule?

Question

Markovnikov's rule states that:

a) addition to an alkene will give the least substituted product.

b) addition to an alkene will give the most highly substituted product.

Could someone explain the answer
Thanks

Answer 1

b)
for example : H2C=CHR + HX
- R is an alkyl
- X is a good leaving group

The first step is the nucleophilic attack of the double bond on the H of HX :
H2C=CHR + HX --> H3C-C(+)HR + X(-)
the secondary carbocation formed is more stable than a primary (formed if the other carbon attacks the H(+)), and a tertiary would be even more stable.
This higher stability is due to hyperconjugation : electrons of the C-C and C-H bonds sigma orbitals of R stabilize the empty p orbital of C(+).
Then the second step is the attack of X(-) on C(+) :
H3C-C(+)HR + X(-) --> H3C-CHRX

The major product formed is called the Markovnikov product. The other (XH2C-CH2R) is called the anti-Markovnikov product (it can be the major product if R is an electron withdrawing group like CF3).

Answer 2

Markovinkov's rule is that when adding H+ ions to a hunk of an organic compound, that H+ will find itself attached to the Carbon that already has the largest amount of H on it that can hold another Hydrogen atom

eg:
CH2=CH-CH3 + HBr --> CH3CHBrCH3
notice how the H+ ion went to the CH2 making it CH3
and how the Br- went where the H+ didn't =P

now chosing between a and b should be easier

Answer 3

I don't like either of the choices for the answer, but the rule suggests that secondary products are favoured over primary ones, so I suppose that the second answer is the better of the two.