6
$\begingroup$

Is the number of hyperconjugation structures for a hydrocarbon with number of 'alpha' hydrogens 'a' equal to 'a' or 'a+1'?

$\endgroup$

1 Answer 1

4
$\begingroup$

Let's use the n-propyl carbocation as an example. It has two hydrogens alpha to the cationic carbon and two resonance structures involving hyperconjugation of those alpha hydrogens can be drawn.

enter image description here

$\endgroup$
4
  • 2
    $\begingroup$ So total number of structures are 3 or 2 as itself is also a structure? $\endgroup$ Jun 22, 2014 at 15:36
  • 3
    $\begingroup$ Total number of resonance structures is 3 $\endgroup$
    – ron
    Jun 22, 2014 at 15:39
  • 2
    $\begingroup$ What about the analogous structure using the C-methyl bond instead of the C-H bond? $\endgroup$
    – jerepierre
    Jun 23, 2014 at 18:41
  • 2
    $\begingroup$ Yes, resonance structures incolving C-C hyperconjugation are also valid resonance structures. In this case, C-C hyperconjugation probably contributes less to the overall picture of the molecule than C-H hyperconjugation. I didn't include such structures since the OP was asking about the alpha-hydrogens. $\endgroup$
    – ron
    Jun 23, 2014 at 18:54

Not the answer you're looking for? Browse other questions tagged or ask your own question.