Concept (explain why this is so..)

Problem # 526

Assign R or S configuration for each molecule below.

a) is straightforward. I've started you off in b).

Problem # 525

On the molecule below, mark each stereocenter with an asterisk. (Note: in some textbooks, stereocenters are referred to as stereogenic centers, chirality centers, or asymmetric centers).

Problem # 522

Let's work through a 1,2 and 1,4 addition. Draw the structures for each of the species in the six boxes below. Also draw curved arrows to show electron movement. 

Problem # 332

Each of the carbocations below will spontaneously rearrange. Draw the structure of the expected rearrangement product.

Problem # 331

Rank the carbocations below in order of decreasing stability. (1 = most stable)

Problem # 320


Let's perform conformational analysis on 2-methylbutane along the C2-C3 bond. We'll use the energy chart given below.


First, draw out the Newman projections along the C2-C3 bond, rotating the front carbon (C-2) by 60 degrees clockwise each time while keeping the back carbon (C-3) stationary.

According to the table above, how much energy does each conformation "cost?"


Second, make a plot of the total energy value for each Newman projection versus its dihedral angle.


Problem # 319

For a molecule to undergo an E2 reaction, the leaving group and the beta-proton must be in an anti-coplanar conformation (one atom straight up, the other straight down). Based on this, which compound undergoes E2 reaction with KOtBu faster? Why?


Problem # 318

Two stereoisomers of trimethylcyclohexane are shown below (compounds A and B). Compare cyclohexane chair forms to determine which isomer has a lower heat of combustion. Explain your reasoning.


Problem # 317


α-D-Glucose is shown below. Draw its two chair forms. Which conformation is more stable? Explain.

I recommend using the common convention wedge = "up" and dash = "down."



Problem # 315


Draw all possible resonance forms for each structure below. Use curved arrows.

Note that some structures only show charge, and not implied protons or lone pairs!