Alkenes and Alkynes Flashcards
What do elements of unsaturation do?
decreases the number of hydrogen atoms
What does E1 reaction entail?
*unimolar reaction to give a carbocation (rate limiting)
*deprotonation by weak base (fast)
*good ionising solvent
*order of reaction like SN1 (3>2>1)
What may E1 be accompanied by?
*hydride shifts
*alkyl shifts
for better stability = better products
What is Zaitsevs rule?
In elimination reactions, the most substituted alkene usually predominates
*major and minor product (90/10 ratio)
What is entailed in E2 reactions?
*more than one species in reaction (bimolar)
*can be a strong base and strong nucleophile
*bulky bases can favour E2 over SN2
What reaction will occur if you have an alkyl halide, strong base/nucleophile?
E2/SN2
What reaction will occur if you have an alkyl halide, weak base/nucleophile?
E1/SN1
What if you have a 1degree alkyl halide, strong and weak base?
strong base/nucleophile = SN2
weak base/nucleophile = NO REACTION
What if you have a 2 degree alkyl halide, strong and weak base/ nucleophile?
strong base/nucleophile = SN2 +E2
weak base/nucleophile = SN1 + E1 (SLOW)
What if you have a 3 degree alkyl halide strong base/nucleophile + weak base/nucleophile?
strong base/nucleophile = E2
weak base/nucleophile = SN1 + E1
what are the methods for synthesis of alkenes?
1 -Dehydrohalogenation of alkyl halides (from alkyl halide to C=C)
2- Dehydration of alcohols
(from alcohol to C=C)
3-Dehydrogenation of alkanes
(from alkane to C=C)
4-Hofmann and Cope eliminations
5-Reduction of alkynes
(from C≡C to C=C)
6-wittig reaction
What are the conditions needed for dehydrohalogenation of alkyl halides?
*base
*heat
*loss of HX
What are the conditions for dehydration of alcohols?
*conc H2SO4
*heat
What are the conditions for dehydrogenation of alkanes?
*heat
*catalyst
What are the conditions for the Hofmann reaction?
*heat
*Ag2O
