Chapter 15: Dienes, Resonance, and Aromaticity

Question 1

Diene

Answer 1

2 double bonds, can be anywhere in the molecule Example: 1,3 butadiene

Question 2

Cumulene

Answer 2

2 double bonds, attached on same carbon atom. Example: 1,2 propadiene (allene)

Question 3

Conjugated diene stability trends: Rank internal double bonds, terminal double bonds, and cumulenes

Answer 3

Most stable: Internal double bonds>terminal double bonds>cumulenes

Question 4

4 atomic orbitals will create ___ hybrid orbitals

Answer 4

4 atomic orbitals will create 4 hybrid orbitals. (n) atomic orbitals will create (n) hybrid orbitals

Question 5

Color is created when electrons move across the ____/_____ gap.

Answer 5

HOMO/LUMO

Question 6

The absorbed color will appear to the eye as the _____ color.

Answer 6

complimentary

Question 7

Diels Alder Reaction: consists of both a ___ molecule, and a ___ molecule.

Answer 7

Consists of both a diene and a dienophile.

Question 8

The Diels Alder reaction is an example of a ___ addition, whose transition state is a concerted _____ reaction.

Answer 8

The Diels Alder reaction is an example of a cycloaddition, whose transition state is a concerted pericyclic reaction.

Question 9

The unit Beta

Answer 9

is about 50 kJ or 12 kcal per mol

Question 10

Trend for wavelength and # of conjugations

Answer 10

The more conjugations, the smaller the energy difference between HOMO and LUMO, so the wavelength increases.

Question 11

Best dienophiles in Diels Alder Reactions:

Answer 11

esters, nitriles, and unsaturated electronegative groups

Question 12

For cyclic compounds in a Diels Alder Reaction, only (cis/trans) double bonds work in six membered rings.

Answer 12

Cis.

Question 13

Stereochemistry of Diels Alder Reaction

Answer 13

syn addition to the dienophile.

Question 14

Endo stereochemistry

Answer 14

R cis to Ro

Question 15

Exo stereochemistry

Answer 15

R trans to Ro