Chapter 13

Question 1

A part of a molecule that involves at least one atom with a p orbital adjacent to at least one π bond. The adjacent atom with the p orbital can be part of another π bond, or a radical, cationic, or anionic reaction intermediate

Answer 1

Conjugated system

Question 2

A substrate involving a three-carbon delocalized carbocation in which the positively charged carbon is adjacent to a carbon-carbon double bond in each of two contributing resonance structures

Answer 2

Allylic carbocation

Question 3

Lewis structures that differ from one another only in the position of their electrons. A single resonance structure will not adequately represent a molecule. The molecule is better represented as a hybrid of all the resonance structures

Answer 3

Resonance structures

Question 4

The carbocation formally related to propene by removal of a proton from its methyl group. The two contributing resonance structures of the delocalized carbocation each include a positive charge on a carbon adjacent to the double bond, such that a p orbital on each of the three carbons overlap to delocalize positive charge to each end of the allyl system

Answer 4

Allyl (propenyl) cation

Question 5

The radical formally related to propene by removal of a hydrogen atom from its methyl group. The two contributing resonance structures of the delocalized radical each include an unpaired electron on a carbon adjacent to the double bond, such that a p orbital on each of the three carbons overlaps to delocalize the radical carbon is adjacent to a carbon-carbon double bond

Answer 5

Allyl radical

Question 6

An effect by which a substituent exerts either an electron-withdrawing effect through the π system of the molecule

Answer 6

Resonance

Question 7

Lewis structures that differ from one another only in the position of their electrons. A single resonance structure will not adequately represent a molecule. The molecule is better represented as a hybrid of all of the resonance structures

Answer 7

Resonance structures

Question 8

A hydrocarbon that contains two double bonds

Answer 8

Alkadiene

Question 9

A hydrocarbon that contains three double bonds

Answer 9

Alkatriene

Question 10

A hydrocarbon with two triple bonds

Answer 10

Alkadiyne

Question 11

A hydrocarbon with a double and triple bond

Answer 11

Alkenyne

Question 12

Highest occupied molecular orbital

Answer 12

HOMO

Question 13

Lowest unoccupied molecular orbital

Answer 13

LUMO

Question 14

A type of optical spectroscopy that measures the absorption of light in the visible and ultraviolet regions of the spectrum. Visible-UV spectra primarily provide structural information about the kind and extent of conjugation of multiple bonds in the compound being analyzed

Answer 14

Ultraviolet-visible (UV-Vis) spectroscopy

Question 15

The distance between consecutive crests (or troughs) of a wave

Answer 15

Wavelength (λ)

Question 16

The number of full cycles of a wave that pass a given point in each second

Answer 16

Frequency (v)

Question 17

The frequency of a wave. Now used instead of the equivalent cycles per second (cps)

Answer 17

Hertz (Hz)

Question 18

The full range of energies propagated by wave fluctuations in an electromagnetic field

Answer 18

Electromagnetic spectrum

Question 19

A plot of the wavelength (λ) of a region of the spectrum versus the absorbance (A) at each wavelength. The absorbance at a particular wavelength (Aλ) is defined by the equation Aλ = log(IR/IS), where IR is the intensity of the reference beam and IS is the intensity of the sample beam

Answer 19

Absorption spectrum

Question 20

A proportionality constant that relates the observed absorbance (A) at a particular wavelength (λ) to the molar concentration of the sample (C) and the length (l; in cm) of the path of the light beam through the sample cell: ε = A/C*l

Answer 20

Molar absorptivity (ε)

Question 21

A principle stating that when the ratio of products of a reaction is determined by relative rates of reaction, the most abundant product will be the one that is formed fastest

Answer 21

Kinetic (or rate) control

Question 22

A principle stating that the ratio of products of a reaction that reaches equilibrium is determined by the relative stabilities of the products (as measured by their standard free energies, ΔG*). The most abundant product will be the one that is the most stable

Answer 22

Thermodynamic (or equilibrium) control

Question 23

The product formed fastest when multiple products are possible; the product formed via the lowest energy of activation pathway

Answer 23

Kinetic product

Question 24

A ring-forming reaction where new bonds are formed to the first and fourth atoms of a molecular moiety, as at the ends of a 1,3-diene in a Diels-Alder reaction

Answer 24

1,4-cycloaddition

Question 25

In general terms, a reaction between a conjugated diene and a compound containing a double bond, called a dienophile, to form a cyclohexene ring.

Answer 25

Diels-Alder reaction

Question 26

A molecule containing two double bonds. In a Diels-Alder reaction, a conjugated diene in the s-cis conformation reacts with a dienophile

Answer 26

Diene

Question 27

The diene-seeking component of a Diels-Alder reaction

Answer 27

Dienophile

Question 28

The product formed by a Diels-Alder [4+2] cycloaddition reaction, so called because two compounds (a diene and a dienophile) are added together to form the product

Answer 28

Adduct

Question 29

Concerted reactions that take place in one step through a cyclic transition state in which symmetry characteristics of molecular orbitals control the course of the reaction

Answer 29

Pericyclic reaction

Question 30

A reaction, like the Diels-Alder reaction, in which two connected groups add to the end of a π system to generate a new ring

Answer 30

Cycloaddition

Question 31

A group on a bicyclic compound that is on the same side (syn) as the longest bridge in the compound

Answer 31

Endo group

Question 32

A group on a bicyclic compound that is on the opposite side (anti) to the longest bridge in the compound

Answer 32

Exo group