Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: jennyjo on March 09, 2005, 01:48:38 AM
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Please help us!! I have a question about monosubstituted cyclohexane. We calculated the % equatorial VS % axial for trimethylsilylcyclohexane and tert-butylcyclohexane. We found that trimethylsilylcyclohexane had a 97% equatorial (which we would have expected to be 100%) and tert-butylcyclohexane was 100% equatorial(which we expected to have a % equatorial less then that of trimethylsilylcyclohexane). We know that Silicon is 150% larger then Carbon ???, so why isn't Silicon 100% equatorial and Carbon is? If you can help it would be much appreciated! Thanks,
jenny
PS we made the calulations with Spartan
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Think about the effect of introducing a silicon in that position: the bond from the carbon in the ring to the silicon will be a lot longer than the bond to the quaternary carbon in the t-butyl case! Think about what the high energy interactions in the axial case are and how they would be affected by the longer C-Si bond.
For reference, C-C bonds are ~154 pm long, which C-Si bonds are ~185 pm.