chapter 10: alkenes

the pi bond is much weaker/stronger than the sigma bond of a C=O, making it more easily broken

weaker

the rotation around the C=O bond is _______

restricted

whenever the two groups on each end of a C=C are different from one another, they can have two kinds of stereochemistry:

trans or trans

trans/cis are more stable than trans/cis

trans are more stable than cis

stability of alkenes increases as the number of r groups on the C=C increases/decreases

increases

alkenes are unsaturated hydrocarbons because

they have fewer than maximum number of hydrogens per carbon

C2H2n

steps to find the degree of unsaturation in a hydrocarbon

1. count the number of carbons and hydrogens in the given atom

2. compare to the alkene that matches

3. subtract alkene Hs from alkane Hs

4. divide by 2

if given the structure, add together the cyclos and double bonds

O atoms = ignore

halogens = 1 H

nitrogen = -1 H

when naming a molecule that contains a double bond and -OH, which has higher priority

the OH

alkenol

if a molecule has two double bonds, what is it called? three?

diene

triene

when naming a cycloalkene

number alkene 1 and 2 and give the first substituent the lowest number

the 1 is omitted

E/Z system

E: highest priorities are opposite of each other

Z: highest priorities are on the same side

1. divide the double bond in half

2. assign priority to substituents

vinyl group

allyl group

alkenes have low/high MP and BP

low

MP and BP of alkenes increase/decrease as number of carbons increase because of increased SA

increase

alkenes are soluble/insoluble in organic solvents and soluble/insoluble in water

soluble in organic solvents

insoluble in water

most alkenes have only _____ IMF

LDFs

the cis isomer of an alkene, yields a _____ dipole , whereas in a trans isomer, the dipoles ____

small net

cancel

cis alkene is more ______, giving it a slightly higher/lower BP

polar

higher

lycopene

red pigment in tomatoes and watermelon

has 13 double bonds

antioxidant → can decrease risk of heart disease and cancer

triaclyglycerols

most abundant lipid

contains 3 ester groups

lipids are water-_______

insoluble

when a triacylglycerol is hydrolyzed it produces

glycerol and three fatty acids

saturated fatty acids have _____ double bonds in their long hydrocarbon chains, and are obtained form ______

no double bonds

animal sources

unsaturated fatty acids have ______ double bonds, and are obtained from ___

one or more

vegetable sources

double bonds in naturally occurring fatty acids have ____ configuration

Z

same side

as the number of double bonds in the fatty acid increases, the MP ______

decreases

fats have _____ MP

fats are derived from FAs having ____ double bonds

higher, solid at room temp

few

oils have ____ MP

oils are derived from FAs having ____ double bonds

lower, they are liquids at room temp

many

alkenes can be prepared from alkyl halides and alcohols via

elimination reactions

the pi bond is much weaker/stronger than the sigma bond, creating the ability for ______ reactions

weaker

addition

every reaction of alkenes involves _______, where the pi bond is _____

addition

broken

because alkenes are electron _____, they react with _______

rich

electrophiles

two types of addition stereochemistry

syn: same side

anti: opposite side

addition reactions are endo/exothermic

exothermic

what can be used to form alkenes

alkyl halides, tosylates, alcohols

markovnikov’s rule

in the addition of HX to an unsymmetrical alkene, the H atom bonds to the less substituted carbon

the H will go to the carbon that will produce the most stable carbocation

might only produce one product because it WONT form a 1 degree carbocation

trigonal planar atoms react with reagents from ___ directions with ____ probability

two

equal

achiral starting materials yield ____ products

racemic

the terms cis/trans refer to:

while syn/anit describe:

arrangement of groups in a particular compound

stereochemistry of a process

hydrohalogenation occurs with _________ addition of HX

syn and anti

in hydration, addition of H and OH occurs in both _______ arrangements

and carbocation formation and rearrangements can/can’t occur

syn and anti

can

halogenation forms a

vicinal dihalide

in halogenation, ____ rearrangements occur, and only _____ addition is produced

no

anti

in halogenation, halonium ions are unstable because

they produce a strained three member ring

in halogenation, the opening of bridged halonium ion intermediates resembles

the opening of epoxide rings with Nu-

steps of halogenation

addition of X+ forms unstable bridged halonium ion

nu- attack of X- occurs from backside to from trans products in anti addition

halohydrin formation

1. addition of electrophile X+ to form bridged halonium ion

2. nu- attack by H2O from backside on three-membered ring

addition of X and OH occurs in anti fashion with trans products being formed

unsymmetrical alkene: two isomers are possible but only the less substituted RX is preferred, thus the OH ends up on the more sub C

no rearrangements

NBS is a source of

Br2

hydroboration

addition of borane (BH3) to an alkene to form alkylborane

oxidation converts C-B bond to C-O bond, retention of configuration

syn addition occurs with no carbocation rearrangements

boron atom bonds to less sub carbon

hydrohalogenation

syn and anti

halohydrin

anti only

halogenation

anti only

hydration

syn and anti

hydroration oxidation

syn only

bonds to less sub

E2

Sn2

E1

Sn1

E2

Sn2

sn2

e2