delocalized pi: dienes & diels-alder

chem 41b wi23 ch.14

what is a conjugated diene? what is not one?

conjugated diene: double bonds separated by a single bond

nonconjugated diene: double bonds not separated at all, or separated by more than one bond

describe the two types of products in a diene reaction with HBr (hydrogen halide). why are two products made?

1. (1,2) haloalkene = kinetic product by proximity
2. (1,4) haloalkene = thermodynamic product by carbocation stability (in juxtaposition with a double bond)

* two products are made because of resonance between the carbocation and double bond

describe how differences in temperature result in favoring one product over the other in diene reactions with hydrogen halides.

add heat: favor equilibrium, increase thermodynamic product

remove heat: favor kinetic product

is the thermodynamic product always (1,4)? is the kinetic product always (1,2)?

no, the thermodynamic product can be either (observe stability); but, the kinetic product is always (1,2)

in a diels-alder reaction, what does the diene act as? what does it react with?

diene acts as a nucleophile, where one double bond reacts with the reactant and the other moves to the single bond that separated the two; it reacts with a dienophile (best when electron poor)

* diels-alder is important because it makes C-C bonds