Orgo Ch. 15 Glossary

Front 1

1,2 addition

Back 1

an addition in which 2 atoms or groups add to adjacent atoms

Front 2

1,4-addition

Back 2

an addition in which 2 atoms or groups add to atoms that bear a 1,4-relationship

Front 3

allyl group

Back 3

common name for 2-propenyl group -CH2-CH=CH2

Front 4

allylic position

Back 4

carbon atom next to a c=c

Front 5

allylic shift

Back 5

isomerization of a DB that occurs through the delocalization of an allylic intermediate (ex. using NBS, hv on an alkene)

Front 6

concerted rxn

Back 6

all bond breaking/making = 1 step

Front 7

conjugated double bonds

Back 7

DBs that alternate w/ single bonds, w/ interaction by overlap of the p orbitals in the pi bonds.

Front 8

isolated double bonds

Back 8

DBs separated by 2+ single bonds. react independently, like simple alkenes.

Front 9

cumulated double bonds

Back 9

successive DBs w/ no intervening single bonds

Front 10

allene (cumulene)

Back 10

a cpd containing cumulated c=c's

Front 11

conservation of orbital symmetry

Back 11

theory of pericyclic rxns stating that the MOs of the reactants must flow smoothly into the MOs of the products w/out any drastic changes in symmetry. = must be bonding (not antibonding) interactions so that the transition state is stable.

Front 12

constructive overlap

Back 12

overlap of orbitals that contributes to bonding. overlap of lobes w/ similar phases is generally constructive overlap

Front 13

cycloaddition

Back 13

rxn of 2 alkenes or polyenes to form a cyclic product. cycloadditions often take place through concerted interaction of the pi electrons in 2 unsaturated molecules.

Front 14

delocalized orbital

Back 14

a molecular orbital that results from the combo of 3+ atomic orbitals. when filled, these orbitals spread electron density over all the atoms involved.

Front 15

destructive overlap

Back 15

overlap of orbitals that contributes to antibonding. overlap of lobes w/ opposite phases is generally destructive overlap.

Front 16

diels-alder rxn

Back 16

synthesis of a 6-membered ring by a [4+2] cycloaddition. this notation means that 4 pi electrons in 1 molecule interact w/ 2 pi electrons in the other molecule to form a new ring

Front 17

dienophile

Back 17

the component w/ 2 pi electrons that reacts w/ a diene in the diels-alder rxn

Front 18

endo rule

Back 18

the stereochemical preference for electron-poor substituents on the dienophile to assume endo positions in a bicyclic diels-alder product

Front 19

secondary overlap

Back 19

overlap of the p orbitals of the electron w/drawing group of the dienophile w/ those of one of the central atoms (C2 or C3) of the diene. This overlap helps stabilize the transition state. w/ cyclic dienes, it favors endo products.

Front 20

heat of hydrogenation

Back 20

the enthalpy of rxn that accompanies the addition of hydrogen to a mole of unsaturated cpd

Front 21

HOMO

Back 21

highest occupied molecular orbital. in a photochemically excited state, this orbital = HOMO*.

Front 22

kinetic control

Back 22

product distribution is governed by the rates at which the various products are formed

Front 23

kinetic product

Back 23

the product that is formed fastest; the major product under kinetic control.

Front 24

LUMO

Back 24

lowest unoccupied molecular orbital

Front 25

molar absorptivity/molar extinction coefficient

Back 25

measure of how strongly a cpd absorbs light at a particular wavelength. it is defined by beer's law A=Ecl

Front 26

molecular orbitals

Back 26

orbitals that include more than one atom in a molecule. molecular orbitals can be bonding, nonbonding, or antibonding

Front 27

bonding MOs

Back 27

MOs that are lower in E than the isolated atomic orbitals from which they are made. electrons here hold the atoms together.

Front 28

antibonding MOs

Back 28

MOs that are higher in E than the isolated atomic orbitals from which they are made. electrons here tend to push the atoms apart.

Front 29

nonbonding MOs

Back 29

MOs w/ the same energy as the isolated atomic orbitals from which they are made. electrons here have no effect on the bonding of the atoms.

Front 30

node

Back 30

a region of an MO w/ zero electron density.

Front 31

pericyclic addition

Back 31

rxn involving concerted reorganization of electrons within a closed loop of interacting orbitals. cycloadditions are one class of pericyclic rxns.

Front 32

reference beam

Back 32

2nd beam in the spectrometer that passes through a reference cell containing only the solvent. the sample beam is compared to this beam to compensate for any absorption by the cell or the solvent.

Front 33

resonance energy

Back 33

the extra stabilization provided by delocalization, compared w/ a localized structured. for dienes and polyenes, the resonance energy is the extra stability of the conjugated system compared w/ the E of a cpd with an equivalent # of isolated double bonds.

Front 34

s-cis conformation

Back 34

a cis-like conformation of a single bond in a conjugated diene or polyene

Front 35

s-trans conformation

Back 35

a trans-like conformation of a single bond in a conjugated diene or polyene.

Front 36

symmetry-allowed

Back 36

the MOs of the reactants can low into the MOs of the products in one concerted step according to the rules of conservation of orbital symmetry. in a symmetry-allowed cycloaddition, there is constructive overlap bt the HOMO of one molecule and the LUMO of the other.

Front 37

symmetry-forbidden

Back 37

the MOs of the reactants are of incorrect symmetries to low into those of the products in one concerted step.

Front 38

thermodynamic control/equilibrium control

Back 38

product distribution is governed y the stabilities of the products. thermodynamic control operates when the rxn mixture is allowed to come to equilibrium.

Front 39

thermodynamic product

Back 39

the most stable product; the major product under thermodynamic control

Front 40

UV-visible spectroscopy

Back 40

the measurement of the absorption of UV and visible light as a fxn of wavelength. UV light = about 100-400 nm. visible = about 400-750.

Front 41

Woodward-Fieser rules

Back 41

a set of rules that correlate values of maximum absorbance in the UV-vis spectrum w/ structures of conjugated systems

Front 42

Woodward-Hoffman rules

Back 42

a set of symmetry rules that predicts whether a particular pericyclic rxn is symmetry-allowed or forbidden.