orgo ch10

diene

has two double bonds

cumulative diene

have adjacent pi bonds with a common sp hybridized carbon, the h atoms at end of the carbon chain are in different planes, can be chiral

isolated diene

double bonds are separated by at least two or more single bonds

conjugated dienes

the double bond is separated by single bond, have conformational and stereoisomers, rotation around cc bond form cis and trans isomers, which can affect reactivity and stability

conjugated s trans vs s cis

s trans is more stable than s cis cause it has lower energy

relative stability of cumulated, isolated, and conjugated diene

conjugated dienes more stable than isolated dienes which are more stable than cumulated dienes cause of resonance stabilization

reaction of conjugated dienes: Add HBr to conjugated diene

form carbocation intermediate that is allylic, form kinetic and thermodynamic product

kinetic product

favored at low temp, it is the more stable carbocation, less stable, forms faster, from 1,2 addition

thermodynamic product

favored at high temp, it is the more sub alkene, more stable, forms slower, from 1,4 addition

pericyclic reactions

one step reaction, no intermediates, requires heat or light and proper mating of symmetry of homo and lumo, are stereospecific

what is cycloaddition reaction

it is between 2 compounds with pi bonds to form cyclic product with 2 new sigma bonds

cycloaddition- diel alder reaction

4 carbon atom diene and 2 carbon atom dienophile combine to form 6 membered ring, 2 reactants are heated, reversible reaction

diel alder reaction- effect of diene formation

the diene must be s cis configuration

diel alder reaction- reaction rate

the e withdrawing group on the dienophile has lower energy of lumo and e donating group on diene raise energy of homo which lower energy gap and inc reaction rate

diel alder- reaction is stereospecific

the relative position of sub in reactants is maintained in product

diel alder reaction- can form bicylic systems

conjugated cyclic dienes where double bonds are locked in s cis formation is highly reactive, formation of bicyclic systems creates endo and exo product

endo product of bicyclic systems

forms faster and is kinetic product as the ts leading to endo product is lower

what is electrocyclic reaction

is reversible reaction that involves ring closure and ring opening

electrocyclic reaction- ring opening

when sigma bonds of cyclic reactant is cleaved to form conjugated product with one or more pi bonds

electrocyclic reaction- ring closure

a intramolecular reaction that forms cyclic product containing one or more sigma bonds and one fewer pi bond than reactant

sigmatropic reaction

rearrangement where sigma bonds break and another sigma bond is formed with reorganization of pi bonds, number of pi and sigma bonds stay the same

sigmatropic- cope rearrangement

cyclic rearrangement of e in 1,5 diene to form more sub double bond, equilibrium lies where there is more sub c

sigmatropic- claisen rearrangement

3,3 rearrangement of vinyl allyl ether or phenyl allyl ether