Is cis or trans faster in E2?

E2 reactions occur most rapidly when the H-C bond and C-LG bonds involved are co-planar, most often at 180o with respect to each other. This is described as an antiperiplanar conformation. The cis- isomer undergoes elimination over 500 times faster than the trans- isomer.

Which conformation is required for the following E2 reaction?

Remember that in order for E2 to occur, the leaving group must be axial. So there’s only one conformation where this will be possible for each ring. However, in the top example, Br is axial only in the least stable conformation, whereas in the bottom example, Br is axial in the most stable conformation.

Is E2 a stepwise or concerted?

E2 reactions are typically seen with secondary and tertiary alkyl halides, but a hindered base is necessary with a primary halide. The mechanism by which it occurs is a single step concerted reaction with one transition state.

Do you have to draw chair conformations every time you do an elimination reaction?

Fortunately, however, you do not need to draw the chair conformations every time when working on an elimination reaction of a substituted cyclohexane. The shortcut here is to remember that the leaving group and the β hydrogen must be on opposite sides of the ring (one on a wedge and the other on a dash or Vice Versa).

How to draw chair conformations of cyclohexane compounds?

Draw the two chair conformations of trans-1-ethyl-4-methylcyclohexane. Label the lower energy conformation. The cyclohexane compounds are mostly expressed and explained in the chair conformations. Cis-trans relation between the substituents is denoted by their axial and equatorial positions.

Which is the best stereoisomer for the E2 transition?

Stereoisomers are particularly suitable in this respect, so the results shown here contain important information about the E2 transition state.

Which is better staggered conformation or antiperiplanar conformation?

This conformation positions the σ bonds that are being broken in the correct alignment to become the π bond. The staggered, antiperiplanar alignment is preferred because it aligns the two σbonds that become the π bond.