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conformational isomers

Discussion in 'DAT Discussions' started by bumpski20, Jun 14, 2008.

  1. bumpski20

    bumpski20 2+ Year Member

    Sep 2, 2007
    i always get confused between gauche staggered and eclipsed. does anyone know a good way of differentiating between the two?

    also while we are on the subject of organic chemistry, did anyone else learn about gentle h? basically if you convert a carboxylic acid to R-COCl and then use gentle h, it reduces it to an aldehyde. kinda like pcc but its for reducing and it takes an extra step. i havent encountered it in any actual DAT material so im scared if a question comes up about reducing a carb acid to an aldehyde we should assume we cant. im just curious because there always trying to trick us about wether or not we can reduce a carb acid to an aldehyde with pcc (which we obviously cant), but if it just says reduce a carb acid to an aldehyde i know we can, its just not common. has anyone else done rxns with gentle h (i think the h stands for heat but im not sure)?
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  3. lphiewok

    lphiewok ACFAS Member 7+ Year Member

    Aug 19, 2007
    Fort Polk, LA
    hrm i am not too sure what about gauche staggered and eclipsed are confusing you.

    staggered would be when atoms attached to the carbons on the front and back (of hydrocarbon) are not on the same plane (60 degree apart). and eclipsed would be when they are on the same plane (where lines of top left and right are all on the same degree, but they will have to draw little bit off so you can see what's on the back).

    so in staggered, they are all pointing at different directions (3 on the front and 3 on the back) and in eclipsed, 3 atoms of front and back are pointing in the same direction (which will cause hinderance and decrease the stability of the molecule)

    gauche staggered is when non-center carbon atom attached (not a hydrogen) in the front and a carbon atom attached in the back are in staggered position with only 60 degree apart from each other. so although they are more stable than eclipsed position (esp totally eclipsed where these two are on the same plane), they will have some kind of hindrance from that carbon (since they are bigger than H, it'll have some kind of interactions) and it makes gauche poisition little bit less stable than regular staggered position.

    and as far as gentle H, I am sorry but I do not recall anything about it. but thanks for the info haha now i know
  4. mddang

    mddang 5+ Year Member

    Dec 29, 2007
    Houston, TX
    "Gentle H" is probably reffering to LiAl(t-butoxy3)H (lithium aluminum tributoxy hydride) or to H2, Pd, Ba(SO4) and S.

    acid chloride -> aldehyde
  5. klutzy1987

    klutzy1987 StudyingSucks Letsgo Mets 5+ Year Member

    Jan 28, 2008
    New York
    The easiest way to remember it is during an eclipse the sun is blocked completely. Same theing here the two substituents are lined up right behind one another so that there is a steric strain and torsional strain between the substituents. However, gauche is where they are next to each other but not actually touching ( lined up).
  6. bumpski20

    bumpski20 2+ Year Member

    Sep 2, 2007
    ok thanks, I think I get it. it's easy to distinguish on newman projections but for some reason i always get messed up drawing them flat.
  7. chemtopper

    chemtopper online organic/general chem/MCAT/DAT tutor 7+ Year Member

    Mar 3, 2009
    Gauche is a french word which means neighbor or in vicinity .... so gauche is a staggered form in which methyl are at 60 deg with each other ...eclipsed is the one in which methyl separated by zero degree angle
    tommyngu likes this.

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