Chapter 13 Flashcards
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
Conjugated system
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
Allylic carbocation
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
Resonance structures
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
Allyl (propenyl) cation
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
Allyl radical
An effect by which a substituent exerts either an electron-withdrawing effect through the π system of the molecule
Resonance
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
Resonance structures
A hydrocarbon that contains two double bonds
Alkadiene
A hydrocarbon that contains three double bonds
Alkatriene
A hydrocarbon with two triple bonds
Alkadiyne
A hydrocarbon with a double and triple bond
Alkenyne
Highest occupied molecular orbital
HOMO
Lowest unoccupied molecular orbital
LUMO
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
Ultraviolet-visible (UV-Vis) spectroscopy
The distance between consecutive crests (or troughs) of a wave
Wavelength (λ)
The number of full cycles of a wave that pass a given point in each second
Frequency (v)
The frequency of a wave. Now used instead of the equivalent cycles per second (cps)
Hertz (Hz)
The full range of energies propagated by wave fluctuations in an electromagnetic field
Electromagnetic spectrum
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
Absorption spectrum
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
Molar absorptivity (ε)
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
Kinetic (or rate) control
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
Thermodynamic (or equilibrium) control
The product formed fastest when multiple products are possible; the product formed via the lowest energy of activation pathway
Kinetic product
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
1,4-cycloaddition
In general terms, a reaction between a conjugated diene and a compound containing a double bond, called a dienophile, to form a cyclohexene ring.
Diels-Alder reaction
A molecule containing two double bonds. In a Diels-Alder reaction, a conjugated diene in the s-cis conformation reacts with a dienophile
Diene
The diene-seeking component of a Diels-Alder reaction
Dienophile
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
Adduct
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
Pericyclic reaction
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
Cycloaddition
A group on a bicyclic compound that is on the same side (syn) as the longest bridge in the compound
Endo group
A group on a bicyclic compound that is on the opposite side (anti) to the longest bridge in the compound
Exo group
