Home > Organic Chemistry > Cyclohexane Chair Flip

What is the 'true boat' conformation?

Answer 1

See this site.

A cyclohexane (#C_6H_12#) ring can have several possible conformations. The MOST stable is the so-called chair conformation, for which each carbon atom in the ring has an axial and equatorial hydrogen. Axially disposed hydrogens on the same face of the ring (which means that are substituted #1,3# with respect to the carbons) undergo so-called transannular steric interaction.

An alternative conformation is the BOAT conformation (I am afraid my poor google-fu prevents me posting a nice picture, but look at the given website!). Here the cyclohexane ring assumes the shape of a boat. In this conformation, the two, alternate #1,4#-substituted hydrogens, occupy the same physical space, which is of course a very unfavourable steric outcome, so the boat conformer is a very high energy species, with a very short lifetime. Twist boat conformations, which separate these hydrogens are a little lower in energy!

To help you remember all of this, get a set of molecular models, look at cyclohexane ring conformers, and relate them to the website. This requires practice because, in addition to using the model, you also need to be able to represent the conformation on the printed page.

For substituted cyclohexanes, e.g. methylcyclohexane, and more so #Bu^tC_6H_11#, there is a great steric preference for the methyl to be in an equatorial conformation.

Please voice your concerns if I haven't been clear, and I'll try again—or someone else will.

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Answer 2

Madison Anderson

The "true boat" conformation is a molecular geometry where a six-membered carbon ring in a cyclohexane molecule adopts a boat-like shape due to the repulsion between adjacent hydrogen atoms.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.