00:02
This is the answer to chapter 27, problem number six, from the smith organic chemistry textbook.
00:10
And in this problem, we are asked to draw the product of two different paracyclic reactions with regards to the stereochemistry that is developed in the products.
00:25
And so the main rule that's going to govern the stereochemistry of these products is going to be what i've written at the top of the page here, which is that in a conjugated polyene, meaning multiple double bonds, in a conjugated polyene, if there are an odd number of double bonds, then there will be disrotatory rotation.
00:56
And if there are an even number of double bonds, there will be con rotatory rotation.
01:03
Disrotitory means that the two carbons in question rotate in opposite directions.
01:10
Con rotatory means that they rotate in the same direction.
01:14
And so to look at these two examples, for a, we see that in our conjugated diene, we have an odd number, or pardon me, in our conjugated polyene, we have an odd number of, double bonds.
01:31
And so when we draw the movement in these electrons, and i will draw that briefly to make it a little easier to visualize, so the electrons are going to move around.
01:48
Remember this happens as a single step.
01:50
These electrons will form the new bond.
01:53
And so we've closed the ring here.
01:56
So this product is going to have a closed ring.
02:00
It will have two double bonds there and there.
02:04
And then these two methyl groups are going to rotate in different directions.
02:11
So they are both flat in the page and the starting material.
02:14
And in the product, we will draw them cis, because one rotates to clockwise and one rotates counterclockwise.
02:26
Clockwise.
02:28
And so they both end up cyst to each other on the same side of the molecule...