Test 1 Flashcards
allylic carbocation
A carbocation in which the positively charged carbon is allylic
allylic free radical
A free radical in which the unpaired electron is on an allylic carbon
allylic anion
A carbanion in which the negatively charged carbon is allylic
conjugated diene
System of the type C=C-C=C, in which two pairs of doubly bonded carbons are joined by a single bond. The pi electrons are delocalized over the unit of four consecutive sp2-hybridized carbons
conjugated systems
A structural arrangement in which electron delocalization permits two groups to interact so that the properties of the conjugated system are different from those of the separate groups.
allylic carbon
The sp3-hybridized carbon of a C=C-C unit. Atoms or groups attached to an allylic carbon are termed allylic substituents.
Hückel’s rule
Completely conjugated planar monocyclic hydrocarbons possess special stability when the number of their pi electrons = 4n + 2, where n is an integer.
lowest unoccupied molecular orbital (LUMO)
The orbital of lowest energy that contains none of a molecule’s electrons; the lowest unoccupied molecular orbital.
highest occupied molecular orbital (HOMO)
Highest occupied molecular orbital (the orbital of highest energy that contains at least one of a molecule’s electrons).
isolated dienes
Diene of the type C=C-(C)x-C=C in which the two dbl bonds are separated by one or more sp3-hybridized carbons. Isolated dienes are slightly less stable than isomeric conjugated dienes.
cumulated dienes/ cumulenes/ allenes
Diene of the type C=C=C, in which one carbon has dbl bonds to two others.
resonance energy/delocalization energy/conjugation energy
Extent to which a substance is stabilized by electron delocalization. It is the difference in energy between the substance and a hypothetical model in which the electrons are localized.
elastomers
A synthetic polymer that possesses elasticity
copolymer
Polymer formed from 2 or more different monomers
1,2 addition
Addition of reagents of the type X-Y to conjugated dienes in which X and Y add to adjacent doubly bonded carbons
1,4 addition
Addition of reagents of the type X-Y to conjugated dienes in which X and Y add to the termini of the diene system
kinetic control
Term describing a reaction in which the major product is the one formed at the fastest rate.
thermodynamically controlled reaction
Reaction in which the reaction conditions permit two or more products to equilibrate, giving a predominance of the most stable product
Diels-Alder reaction
Conjugate addition of an alkene to a conjugated diene to give a cyclohexene derivative. Diels-Alder reactions are extremely useful in synthesis.
dienophile
The alkene that adds to the diene in a Diels-Alder reaction.
cycloaddition
Addition, such as the Diels-Alder reaction, in which a ring is formed via a cyclic transition state.
pericyclic reactions
A reaction that proceeds through a cyclic transition state.
endo/Alder rule
The preferred product in a Diels/Alder reaction where the interaction between the developing pi bond and the carbonyl groups present stablizes the dienophile as it is approaching. This results in the “outside” groups on the diene on the SAME side of the 6-membered ring as the electron withdrawing group (EWG).
frontier orbitals
Orbitals involved in a chemical reaction, usually the highest occupied molecular orbital of one reactant and the lowest unoccupied molecular orbital of the other.
symmetry-allowed reaction
Concerted reaction in which the orbitals involved overlap the phase at all stages of the process
symmetry-forbidden
Concerted reaction in which the orbitals involved do not overlap in phase at all stages of the process
Cope rearrangement
The thermal conversion of the 1,5-diene unit to another by way of a cyclic transition state.
arene
Aromatic hydrocarbon. Often abbreviated ArH.
aromaticity
Special stability associated with aromatic compounds.
aliphatic hydrocarbon
Term applied to compounds that do not contain benzene or benzene-like rings as a structural unit. (Historically, aliphatic was used to describe compounds derived from fats and oils.)
Kekulé structure
Structural formula for an aromatic compound that satisfies the customary rules of bonding and is usually characterized by a pattern of alternating single and double bonds. There are two Kekulé formations for benzenes: dbl bonds between C1=C2, C3=C4, C5=C6 or C2=C3, C4=C5, C6=C1. A single Kekulé structure does to completely describe the actual bonding in a molecule.
Closed-shell electron configuration
Stable electron configuration in which all the lowest energy orbitals of an atom (in the case of the noble gases), an ion (e.g. Na+), or a molecule (e.g. benzene) are filled.
ortho-
Term describing a 1,2 relationship between substituents on a benzene ring.
meta-
Term describing a 1,3 relationship between substituents on a benzene ring.
para-
Term describing a 1,4 relationship between substituents on a benzene ring.
phenyl
A benzene ring with 5 hydrogens and 1 methyl or R-group attached. It is often abbreviated C6H5–.
benzyl group
The group C6H5CH2–.
polycyclic aromatic hydrocarbon
An aromatic hydrocarbon characterized by the presence of two or more fused benzene rings.
Birch reduction
Reduction of an aromatic ring to a 1,4-cyclohexadiene on treatment with a group 1 metal (Li, Na, K) and an alcohol in liquid ammonia.
Frost circle
A mnemonic that gives the Hückel pi molecular orbitals for cyclic conjugated molecules and ions.
annulene
Monocyclic hydrocarbon characterized by a completely conjugated system of double bonds. Annulenes may or may not be aromatic.
[x]annulene
An annulene in which the ring contains x carbons.
heterocyclic compounds
Cyclic compound in which one or more of the atoms in the ring are elements other than carbon. Heterocyclic compounds may or may not be aromatic.
heterocyclic aromatic compounds
A heterocyclic compound in which the ring that contains the heteroatom is aromatic.
