Chemical Forums

Please login or register.

Login with username, password and session length

Sponsored links

Pages: [1]   Go Down

Author Topic: organic compound acidity of sp hybridized bonds  (Read 6235 times)

0 Members and 1 Guest are viewing this topic.

briteyellowness

  • Guest
organic compound acidity of sp hybridized bonds
« on: August 11, 2005, 04:18:09 PM »

why are sp hybridized C-H bonds more acidic than sp2 C-H bonds which are more acidic than sp3 C-H bonds?
Logged

Yggdrasil

  • Retired Staff
  • Sr. Member
  • *
  • Mole Snacks: +447/-20
  • Offline Offline
  • Gender: Male
  • Posts: 3027
  • Physical Biochemist
Re:organic compound acidity of sp hybridized bonds
« Reply #1 on: August 11, 2005, 09:32:19 PM »

It all depends on the s character of the bond.  Think about the molecular orbitals.  The electrons in the s orbital are more tightly bound to the nucleus, while electrons in the p orbitals are more inclined to be shared between atoms (e.g. in pi bonds).  Therefore, electrons in molecular orbitals with a high s character are less inclined to be shared between atoms.  If electrons are less inclined to be shared, the bond formed by those electrons is weaker and more easily broken.  So, in a terminal alkene, which contains a bond between an sp-hybridized carbon (50% s character) and a hydrogen, the bond is easily broken because of the carbon's high s character, resulting in a relatively high acidity (pKa ~20).  However, in a bond between an sp3-hybridized carbon (25% s character) and a hydrogen, the bond is much stronger, resulting in very low acidity (pKa ~50-60).
Logged

Winga

  • Chemist
  • Full Member
  • *
  • Mole Snacks: +39/-10
  • Offline Offline
  • Posts: 510
Re:organic compound acidity of sp hybridized bonds
« Reply #2 on: August 11, 2005, 09:38:42 PM »

sp hybridization = 50% s-character, 50% p-character
sp2 hybridization = 33.3% s-character, 66.7% p-character
sp3 hybridization = 25% s-character, 75% p-character

s-orbital is closer to nucleus than p-orbital comparing with same shell.
Moreover, more the s-character, more electronegative of that (carbon) atom.

Therefore, sp hybridized C withdraws the bonding e- closer to itself and it is easier to deprotonate.
Logged
Pages: [1]   Go Up
 

Mitch Andre Garcia's Chemical Forums 2003-Present.

Page created in 0.052 seconds with 23 queries.