IIT JEE , AIEEE Forum - Chemistry , Organic Chemistry

srini

hey

if a six membered ring is more stable than a seven,then no expasio would take place?

srini

hey

some one? answer

a5hw1n_5

Actually expansion would take place, but the structure would loose it its planar structure to form puckered 3d rings hence decreasing its strain and increasing its stabilty.

srini

hey

so the expansion takes place?

khinart

The expansion would never take place because in doing so the ring would lose its aromaticity(if aromatic) or may even lose its stability(if it has no double bonds) which is impossible

srini

hey

friend,then in case of cyclohexane?

beck2ham

see srini, in case of cylclohexane(which is even more stable than benzene), on ring expansion, you would get a seven mebered ring which isn't very stable .......thus, never ever even think of ring expansion in cylcohexane...

Though, it might undergo ring contraction to form a five or a four membered ring..

arsenal2007

it all depends upon the alpha hydrogen at the carbocation

plz rate me if you are satisified

madhusudan.chavan

The rings containing five or less carbon atoms are either planar or nearly planar, but those of six and more carbon atoms are essentially non-planar or puckered. As a result, each carbon atom retains its normal tetrahedral angle and there is negligible or no strain in the molecule

The stability of the rings is determined from the heat of combustions. For cyclohexane the heat of combustion is 657.9 same as that for n-alkanes, hence is more stable. Rings containing 7-11 carbon atoms are almost as stable as cyclopentane since they have the same value for heat of combustion per CH2 group(663.4-662.1).The heats of combustion per CH2 group of cyclohexane and rings containg 12 or more carbon atoms are about the same(658.8-657.1) as that of alkane. Hence cyclohexane and rings containg 12 or more carbon atoms are as stable as n-alkanes.

Ask & Discuss Questions with Community & Experts