Dismiss Notice
Check out the new Application Assistant, where you can calculate your LizzyM score, see how you rank compared to other applicants, and see a list of schools where similar students were accepted.
Dismiss Notice
Visit Test Prep Week: Test Prep Week 2016 is happening NOW! Come to the Exhibition Forums for raffles and information about test prep services and vendors.

Organic Chemistry Question

Discussion in 'MCAT Discussions' started by roycer, 06.26.07.

  1. SDN is made possible through member donations, sponsorships, and our volunteers. Learn about SDN's nonprofit mission.
  1. roycer

    roycer 2+ Year Member

    Joined:
    04.09.07
    Messages:
    267

    SDN Members don't see this ad. About the ads.
    What is the hybridization of the nitrogen in pyrrole?:

    http://upload.wikimedia.org/wikipedia/commons/thumb/1/15/Pyrrole.png/300px-Pyrrole.png

    Is it sp3 or sp2 because it is a conjugated system?
     
  2. SDN Members don't see this ad. About the ads.
  3. LC17

    LC17 2+ Year Member

    Joined:
    03.27.07
    Messages:
    20
    Status:
    Pre-Medical
    sp3
     
  4. saqrfaraj

    saqrfaraj Pediatric Pulmonology 7+ Year Member

    Joined:
    05.16.07
    Messages:
    2,296
    Location:
    PFT Lab
    Status:
    Fellow [Any Field]
    Verified
    Physician
    No, it's sp2. The nitrogen is bound to two carbons, one hydrogen, and the lone pair is in the empty p-orbital.
     
  5. roycer

    roycer 2+ Year Member

    Joined:
    04.09.07
    Messages:
    267
    sp2 is what I figured too. Kaplan says it is sp3 for some reason, and that the sp3 hybridized orbitals overlap with the p-orbitals of the other carbons to form the conjugated ring. That just sounds wrong.
     
  6. MystA RavE

    MystA RavE 7+ Year Member

    Joined:
    02.22.07
    Messages:
    219
    Location:
    Brooklyn, NY
    Status:
    Resident [Any Field]
    Its sp3, NOT sp2. There are 4 regions of electron density due to the lone pair of electrons on the N.
     
  7. saqrfaraj

    saqrfaraj Pediatric Pulmonology 7+ Year Member

    Joined:
    05.16.07
    Messages:
    2,296
    Location:
    PFT Lab
    Status:
    Fellow [Any Field]
    Verified
    Physician
    First, you don't count lone pairs when figuring out the hybridization. Secondly, the nitrogen is attached to two carbons which are both sp2 hybridized and therefore must also be sp2 hybridized if it is to overlap for maximum stability.
     
  8. riceman04

    riceman04 10+ Year Member

    Joined:
    03.21.05
    Messages:
    8,511
    Location:
    Los Angeles
    Status:
    Medical Student
  9. roycer

    roycer 2+ Year Member

    Joined:
    04.09.07
    Messages:
    267
    Since pyrrole is conjugated, it also must be planar. My reasoning is that the nitrogen is sp2 hybridized (2 sp2 orbitals are bonded to an adjacent carbon and 1 sp2 orbital is bonded to the hydrogen) forming a planar geometry. The lone pair of electrons is in a nonhybridized p-orbital perpendicular to this plane and conjugated with the p-orbitals of the other carbons (which are also sp2).
     
  10. scotties123

    scotties123 GrandMacDaddy 7+ Year Member

    Joined:
    04.29.07
    Messages:
    565
    Status:
    Medical Student
    to calculate hybridization you do: # of lone pairs + # of sigma bonds. Therefore, 1+3=4 --> sp3
     
  11. saqrfaraj

    saqrfaraj Pediatric Pulmonology 7+ Year Member

    Joined:
    05.16.07
    Messages:
    2,296
    Location:
    PFT Lab
    Status:
    Fellow [Any Field]
    Verified
    Physician
    Okay, guys. We know pyrrole is aromatic so it needs the lone pair on the nitrogen to get the necessary six electrons. To form the conjugated system, the lone pair has to be in the plane above the atoms. This cannot happen if the nitrogen is sp3 hybridized. It MUST be sp2 hybridized to be aromatic.
     
  12. EECStoMed

    EECStoMed Persistence > Intel 2+ Year Member

    Joined:
    02.25.07
    Messages:
    339

    It is SP3 no doubt, but can undergo sp2 hybridization, which is what it does. Who the hell said that you don't count lone pairs when doing hybridization? What would that make ammonia then?
     
  13. koopa_troopa

    koopa_troopa Junior Member 7+ Year Member

    Joined:
    03.28.05
    Messages:
    288
    Status:
    Medical Student
    Roycer, you are correct, it is sp2. If you still have your organic chem text book you can check it out, this is a fairly common example in any aromatic compound chapter.
     
  14. saqrfaraj

    saqrfaraj Pediatric Pulmonology 7+ Year Member

    Joined:
    05.16.07
    Messages:
    2,296
    Location:
    PFT Lab
    Status:
    Fellow [Any Field]
    Verified
    Physician
    Yes, the four things attached to nitrogen would give an sp3 hybridization but pyrrole is aromatic and so the nitrogen has to become sp2 hybridized. So when talking about the aromatic molecule wouldn't we say it's sp2?

    When I said you don't count the lone pair, I only meant in this case because it has to be up in the plane above the atoms. I was just trying to conceptually explain how the three OTHER things contributed to the trigonal planar character. I admit, I didn't word it right.
     
  15. spicedmanna

    spicedmanna In Memory of Riley Jane Moderator Emeritus 2+ Year Member

    Joined:
    08.22.06
    Messages:
    5,823
    Location:
    KC, MO
    Status:
    Resident [Any Field]
    The nitrogen in the ring is clearly sp2 hybridized. Normally, the nitrogen would be sp3 hybridized, but it must rehybridize to sp2 so that the lone pair of electrons can be delocalized into the pi-system of the ring and that the molecule can be aromatic. What we see here is that aromaticity is highly favored.
     
    lamt1220 likes this.
  16. scotties123

    scotties123 GrandMacDaddy 7+ Year Member

    Joined:
    04.29.07
    Messages:
    565
    Status:
    Medical Student
    ok, i just googled it and checked a few different websites. The ones i checked seem to agree that BENZENE is sp2. I assume because of its aromaticity, that pyrrole would also be sp2. Good thing i learned this now and not after taking the mcat:laugh:
     
  17. roycer

    roycer 2+ Year Member

    Joined:
    04.09.07
    Messages:
    267
    Thank you. sp2 it is. :)
     
  18. killinsound

    killinsound 7+ Year Member

    Joined:
    08.30.06
    Messages:
    909
    Status:
    Resident [Any Field]
    Verified
    Physician
    1. yes you do

    2. that doesn't make sense. if you had propene, one of the carbons is still sp3 hybridized



    lastly, someone said something about pyrrole being planar so it had to be sp2... the nitrogen could have the two carbon bonds in one plane and the lone pair and the hydrogen in another making it Sp3.

    however, aromaticity always prevails and for this reason alone, the nitrogen must donate its e- into the ring making it Sp2.
     
  19. saqrfaraj

    saqrfaraj Pediatric Pulmonology 7+ Year Member

    Joined:
    05.16.07
    Messages:
    2,296
    Location:
    PFT Lab
    Status:
    Fellow [Any Field]
    Verified
    Physician
    1. Yep. I know you do. Check up a few posts.
    2. Propene is not an aromatic ring. We're talking ring stability.
     
  20. powerful_squib

    powerful_squib Snoop dogg resident 2+ Year Member

    Joined:
    10.17.06
    Messages:
    285
    Location:
    New Jersey
    Status:
    Pre-Medical
  21. saqrfaraj

    saqrfaraj Pediatric Pulmonology 7+ Year Member

    Joined:
    05.16.07
    Messages:
    2,296
    Location:
    PFT Lab
    Status:
    Fellow [Any Field]
    Verified
    Physician
    Even if you had it that way, the lone pair wouldn't be sticking straight up at 90 degrees so I don't think it'd work. It needs to be sp2 for it to be aromatic.
     
  22. roycer

    roycer 2+ Year Member

    Joined:
    04.09.07
    Messages:
    267

    I completely agree with you saqrfaraj. Aromaticity gives molecules special stability due to the parallel overlap of p-orbitals. It just wouldn't work if the nitrogen was sp3 hybridized.
     
  23. J DUB

    J DUB Watch my TAN walk!! Lifetime Donor 10+ Year Member

    Joined:
    08.01.05
    Messages:
    57,543
    Location:
    working on my tan......
    Status:
    Medical Student
    Verified
    Pharmacist
    Rocket
    Scientist
    Correct answer above: sp2

    since the lone pair of electrons on the nitrogen delocalize into the aromatic ring, if it were not aromatic, then it would be sp3.
     
  24. BrokenGlass

    BrokenGlass 2+ Year Member

    Joined:
    01.12.07
    Messages:
    1,403
    Status:
    Non-Student

About the ads

Share This Page