This is a long, graphics intensive post. You probably don't need to read it all now, but chances are, you'll REALLY need to know the skill I describe here soon. Because it's an extremely common question found on The First Midterm. What this post teaches you how to do is to calculate the energies … [Read more...]
Newman Projections
Imagine you have a clock. Not a digital clock. One of those old fashioned clocks with two hands. Let's try something. Make the clock show high noon, so that both hands are pointing at 12. Now pin down down the hour hand so it can't move. (Or if you want, pin down the minute hand. Either one, … [Read more...]
Conformations
You've likely learned by now that you can rotate single bonds ("sigma bonds") but you can't rotate multiple bonds (Pi bonds). Now we can start talking about some of the consequences of this. A molecule with single bonds - an alkane, let's say - has a certain amount of freedom in how its bonds … [Read more...]
Bredt’s Rule (And Summary of Cycloalkanes)
At the beginning of this series on cycloalkanes we saw that carbon's ability to form rings leads to all kinds of interesting consequences that follow logically from the rules of structure and bonding in organic chemistry, but nevertheless would have been hard to predict from first principles. Among … [Read more...]
Bridged Bicyclic Rings (And How To Name Them)
In the previous post we started our discussion of structures with more than one ring, using decalin as our key example of a fused ring. We saw how much the stereochemistry at the ring junction can affect the overall shape of the molecule, as well as its stability. Fused Rings, Bridged Bicyclic … [Read more...]
Fused Rings
At the beginning of this series I said that the fact that carbon can form rings leads to all kinds of interesting consequences. We're going to see many examples of that in our post today! So far, we've only talked about cyclic molecules containing one ring. But, of course, molecules with multiple … [Read more...]
Which Cyclohexane Chair Is Of Lower Energy?
In the last post, we introduced A values and said they were a useful tool for determining which groups are "bulkiest" on a cyclohexane ring. The greater the A-value (bulk), the more favoured the equatorial conformer will be (versus axial). We saw that hydroxyl groups (OH) have a relatively low … [Read more...]
Substituted Cyclohexanes: “A Values”
In the last post we saw that adding a methyl group to cyclohexane results in two chair conformers that are unequal in energy. We saw that the conformer where the methyl group was equatorial is the most stable, since it avoids destabilizing diaxial interactions (technically, gauche interactions) that … [Read more...]