Oc(5)Alkenes & Alkynes

Front 1

formula for number of double bonds in an alkene

Back 1

N=1/2 (2n+2-m) of C_nH_m

Front 2

olefins

Back 2

alternate name for alkenes

Front 3

alkene physical properties

Back 3

similar to alkanes
mp and bp increases with increasing molecular weight

terminal alkenes have a lower bp than internal alkenes

trans have a higher mp than cis due to packing in solid state

trans have lower bp than cis since they are less polar

Front 4

alkene synthesis via elimination reactions

Back 4

alkanol + base/heat = alkene + H2O

acyl halide + acid/heat = alkene + HX

Front 5

E1 mechanism

Back 5

Unimolecular elimination

1. leaving group departs, producing a carbocation
2. a proton is removed by a base, forming the double bond

favored by highly polar solvents, highly branched carbon chains, good leaving groups, and weak nucleophiles in low concentration

Front 6

E2 mechanism

Back 6

bimolecular elimination

one step: a strong base removes a proton, while a halide ion anti to the proton leaves, resulting in the formation of a double bond

more sub'ed bond is prefered

favors highly sub'ed carbon chains, strong bases, high concentration

Front 7

catalytic hydrogenation

Back 7

reductive process of adding molecular hydrogen to a double bond with the aid of a metal catalyst

syn addition of the hydrogens, added on same side of the double bond

typical catalysts: platinum, palladium, nickel

Front 8

electrophilic addition reactions

Back 8

electrons of the pi bond are exposed and are easily attacked by electrophiles

Front 9

addition of HX

Back 9

electrophilic addition

1. double bond reacts with a proton, yielding a carbocation
2. halide ion combines with the carbocation to give the acyl halide

forms most stable carbocation-Markovnikov's Rule

Front 10

Markovnikov's Rule

Back 10

refers to the addition of something (e.g. halide, hydroxyl group) to the most subs carbon in the double bond.

the addition of a protic acid HX to an alkene, the acid hydrogen (H) becomes attached to the carbon with fewer alkyl substituents, and the halide (X) group becomes attached to the carbon with more alkyl substituents.

Front 11

addition of halogen X2

Back 11

electrophilic addition

double bond acts as a Nu and attacks X2 leaving X-, intermediate carbocation forms a cyclic halonium ion, X- attacks forming the dihalo compound

anti addition, two added groups are on opposite sides of the double bond

can produce a halo alcohol if carried out in a Nu solvent like water

Front 12

addition of water

Back 12

electrophilic addition

water added under acidic conditions

double bond is pronated according to Markovnikov, carbocation reacts with water, forming a pronated alcohol which is depronated to an alcohol

favored at low temp
--the reverse rxn is acid-catalyzed dehydration favored by high temps.

often done via mercuric acetate (Hg(CH3COO)2) to better control yields

Front 13

free radical addition

Back 13

addition of HX to alkenes in the presence of peroxides, causing radical X to form

antiMarkovnikov, X attacks first at the least sub'ed site, forming the most sub'ed radical

Front 14

hydroboration

Back 14

Reactants: Diborane (B2H6) + Alkene
Reagents: 1. BH3 2. H2O2/OH-
Product: OH, anti-marko, syn

Diborane adds to db. B acts as NUC (LA) and attacks less subs C. Than oxidation-hydrolysis w/ perioxide and aq base to produce OH.

Front 15

oxidation with potassium permanganate (2 diff. products)

Back 15

Alkenes + (cold,dilute,KMnO4) --> 1,2 diols (vicinal diols) w/ syn orientation.

nonterminal Alkene + (1.KMnO4,OH-,heat 2. H+) --> 2 M COOH
---if bonded C is disubs'ed than ketone will form.

terminal alkenes + (1.KMnO4,OH-,heat 2. H+) --> COOH + CO2

Front 16

oxidation by ozonolysis

Back 16

alkene + 1)O3, CH2Cl2, 2)Zn/H20 = cleavage to aldehyde

if the rxn is reduced with NaBH4/CH3OH, corresponding alcohols are produced

Front 17

oxidation by peroxycarboxylic acids (CH3CO3H)

Back 17

forms oxiranes/epoxides

CH3CO3H and m-chloroperoxybenzoic acid (mcpba) are often used

Front 18

polymerization of alkenes

Back 18

radical mechanism which requires high temp and pressures.

forms long polymer alkanes from alkene monomers

Front 19

physical properties of alkynes

Back 19

similar to analogous alkanes and alkenes

internal alkynes has higher bp than terminal alkynes.

shorter chain alkynes are gases

solutions are slightly polar
terminal alkynes are fairly acidic

Front 20

synthesis of alkynes

Back 20

elimination of two molecules of HX from a geminal or vicinal dihalide via heat and a strong base

a terminal triple bond is converted to a Nu by removing an acidic proton with a strong base, producing an acetylide ion. this performs Nu displacements on alkyl halides at room temp, lengthening the alkyne

Front 21

reduction of alkynes

Back 21

Lindlar's catalyst (Pd/BaSO4 and quinoline)- hydrogenation of alkynes that stops the rxn at an alkene product cis isomer.

Na/NH3- produces trans alkene isomer from an alkyne

Front 22

electrophilic addition of alkynes

Back 22

same as in alkenes
follows Markovnikov's rule
1. add X
2. add H
rxn can be stopped at alkene or allowed to continue to alkane

Front 23

free radical addition of alkynes

Back 23

same as in alkenes
anti-Markovnikov orientation
1. add H+
2. add X-
trans isomer product

Front 24

hydroboration of alkynes

Back 24

same as in alkenes

syn addition, can form cis alkenes

the B atom can be replaced w/ a proton from acetic acid to produce cis alkene.

w/ terminal alkynes, a disubs'ed B is used to limit boration of the vinylic intermediate - can be oxidatively cleaved w/ peroxid creating OH which rearranges to more stable carbonyl ---keto enol tautomerism.

Front 25

oxidation of alkynes

Back 25

1)KMnO4, OH-
2) H+ (acidification)
yields two carboxylic acids of equivalent molar weight

or

1)O3, CCl4 (ozone)
2) H20
yields: a carboxylic acid and an aldehyde

Front 26

Are double bonds functional groups?

Back 26

Yes, makes alkenes more reactive compared to alkanes.

Front 27

General formula for a straight chain alkened w/ one double bond

Back 27

CnH2n

Front 28

Nomenclature of Alkenes

Back 28

described by cis, trans, E, Z.

Front 29

What are the common names of ethene, propene, 2methyl1propene?

Back 29

ethylene, propylene, isobutylene

Front 30

Substitution and Elimination Reaction Overview

Back 30

1' alkyl halide react via Sn2.

2' alkyl halides go Sn2 w/ small, strong NUC; strong bases go E2.

3' alkyl halides favor E2 w/ SB; Sn1 and E1 w/ WB.

Front 31

Reactions where one stereisomer is favored are termed?

Back 31

stereospecific rxns