orgo 3, 4, 5

olefins
alkenes
alkenes
hydrocarbons that contain a C-C double bond (common)
alkynes
hydrocarbons that contain a C-C triple bond (rare)
unsaturated
alkenes/alkynes have fewer hydrogens per carbon
suffix for alkenes
-ene
suffix for alkynes
-yne
hybridization of carbons in double bond
3 sp2 hybrid orbitals
120 degree plane
p orbital perpendicular to sp2 plane
1 sigma, 1 pi bond
does free rotation occur in double bonds?
no, pi bonds need to be broken first
cis
methyl groups are on the same side of the double bond
less stable because of steric strain
in the presence of acid changes to trans
trans
methyl groups are on different sides of the double bond
cis-trans isomerism can’t occur if…
if one of the double bond’s carbon is attached to 2 identical groups
use EZ naming instead of cis-trans when…
double bond has 3 or 4 different substituents
E
higher ranked groups are on opposite sides of double bond
Z
if higher ranked groups are on the side side of the double bond
Cahn-Ingold-Prelog rules
rank groups by atomic number

if decision can’t be made by first atoms, look at second atoms ect. until you can find difference

multiple bonded atoms are equal to same number of single bonded atoms

addition reaction
occur when two reactants add to form a single, new product with no atoms left over
elimination reactions
single reactant splits into two products, mostly a small molecule like H2O or HCl
substitution reactions
occur when two reactants exchange parts to yield two products
rearrangement reactions
occur when a single reactant undergoes a reorganization to yield a single isomeric product
reaction mechanism
how a reaction occurs through bonds breaking/forming, relative rates, how electrons move/reorganize
how can a covalent bond break?
symmetrical, unsymmetrical
symmetrical break
covalent bond breaks so that one electron remains with each product fragment
unsymmetrical break
covalent breaks so that both electrons remain with one fragment, leaving other fragment with vacant orbital
homolytic
symmetrical cleavage
heterolytic
unsymmetrical cleavage
half-headed/fish-hook arrow
shows the movement of one electron

symmetrical bond-breaking (radical)

full-headed arrow
shows the movement of two electrons

unsymmetrical bond-breaking (polar)

symmetrical bond-making
radical

one bonding electron is donated by each reactant

unsymmetrical bond-making
polar
two bonding electrons are donated by one reactant
radical reactions
symmetrical

movement of single electrons

free-radicals

polar reactions
electrons move in pairs

more common reaction type

occur due to partial pos/neg charges in molecule

polar bonds
made when electron rich atom shares a pair of electrons with electron poor atom
polar bonds break when…
one atoms leaves with both electrons from the former bond
red electrostatic potential map
electron rich (-)
blue electrostatic potential map
electron poor (+)
curved arrow
indicates movement of electrons
nucleophile
nucleus loving

attracted to positive charge

electron rich (-)

neg/neutrally charged

lone pairs (lewis base)

NH3, water, OH-, Cl-

electrophile
electron loving

electron poor (+)

forms bonds by accepting electrons (lewis acid)

pos/neutrally charged

are sigma bonds reactive?
NO! that’s why alkanes aren’t reactive because they only have 1 sigma bond
pi bonds
reactive

above/below the plane of the molecule

it’s electron pair behaves as a nucleophile (base)

carbocation
positively charged intermediate specie in a reaction

electrophile

energy diagrams
graphically depicts energy changes that occur during a reaction
vertical axis of energy diagram
represents total energy of all reactants
horizontal axis of energy diagram
represents progress of reaction

reaction co-ordinate

reactants (A)
energy of the reactants at the start

new C-H bond begins to form and H-Cl bond begins to break

why does energy increase when two reactants collide?
electron clouds repel each other
what is required for a reaction to start?
proper orientation and sufficient force of collision
first transition state (B)
structure of maximum energy

can’t be isolated/directly observed

c=c pi bond is partially broken and new C-H bond is partially formed

activation energy (E act)
energy difference between reactants (A) and transition state (B)

measures how rapidly reaction occurs

large E act
slow reaction
small E act
fast reaction
carbocation (C)
energy of the carbocation

C-H bond is fully formed

reaction intermediate

entity that is formed during a reaction that reacts further

second transition state (D)
C-Cl bond is partially formed

has its own activation energy E act2

products (E)
energy of the products

C-Cl bond is fully formed

(F)
difference in energy between reactants and products
energy releases
reactants has more energy than products
energy absorbs
products have more energy than reactants
catalyst
used as an alternate mechanism when E act can’t be reached

takes part in reaction, regenerates, goes under no net change

increases overall rate of reaction by providing a different pathway

hydrogenation
reaction of alkenes with hydrogen
enzymes
biological catalysts

E act has to be low for biological reasons

manipulate reaction by providing series of small steps

uncatalyzed reactions have…
large activation energies
regiospecific reactions
reaction where HX is added to alkenes where a mixture is not obtained

obeys markovnikov’s rule

morkovnikov’s rule
H attaches to the carbon with more H’s and X attaches to the carbon with more substituents

if both carbons have the same # substituents= mixture

carbocations
planar (attack can happen on both sides of plane equally well)

pos carbon is sp2

3 substituents are oriented in an equilateral triangle

6 valance e- are used for the 3 sigma bonds

p orbitals are above/below plane

p orbital is vacant

alkyl groups donate e- to pos carbon

p orbital of carbocations are….
vacant

above/below plane

where do alkyl groups donate their e- to?
positively charged carbon atom
most stable carbocation
most substituted

attached to more electron rich atom (primary, secondary, tertiary)

lower energy

rank carbocations by increasing stability
methyl, primary, secondary, tertiary
hydration
h2o adds to alkenes to yield alcohols

takes place on treatment of alkenes with water and strong acid

protonated alcohol
final alcohol with a proton

second carbocation in hydration

hydration reaction conditions are severe because…
strong acid and high temperatures are used

causes sensitive molecules to be destroyed

biological hydration requirements
double bond to be next to carbonyl group

enzyme fumarase to help with hydration during food metabolism

halogenation
halogens, such as Br2 and Cl2, are readily added to alkenes

trans

what does Br2 test for
presence of double bonds
anti-stereochemistry
halogenation of alkenes results in trans orientation

bromine ties up one face of the ring, forcing the other bromine to the opposite side

anti=stereochemical outcome of reaction, not stereochemistry

planar carbocation + Br2 –>
mixture
haloperoxidases
enzymes that carry out halogenation in marine organisms
hydrogenation
addition of hydrogen to an alkene

needs a catalyst

heterogeneous process (catalyst doesn’t dissolve)

occurs on surface of catalyst

reduction
hydrogenation

addition of H -or- removal of O

adsorption
physical process

molecules/atoms stick to surface of catalyst

complexation
chemical process

pi electrons in alkene interact with metal through complexation

syn stereochemistry
reduction/hydrogenation

cis orientation

oxidation
addition of O -or- removal of H
oxidized alkenes yield..
epoxides
epoxide
cyclic ether with an oxygen atoms in a three membered ring

occurs by treatment of peryoxide, RCO3H

epoxides
oxiranes
hydrolysis
reaction where epoxides undergo acid-catalyzed ring opening reaction with water
diol
product of hydrolysis

AKA dialcohol

glycols
diols
hydroxylation
process of epoxidation followed by hydrolysis

addition of -OH to each carbon of C=C

trans, one face of double bond is blocked

trans

why does protonation of epoxide make it more reactive?
C-O bond becomes more polar because of pos charge, susceptible to attack by water
hydroxylation of alkene in a single step
react alkene with KMnO4 in a basic solution

cis-diol

cleavage

cleavage
separation of double bond (KMnO4 acidic)
what functional groups are contained after cleavage?
carbonyls
double bond that is tetra-substituted after cleavage…
2 ketones
if 1 hydrogen is on the double bond after cleavage…
one product is a carboxylic acid
if 2 hydrogens are present on 1 carbon of double bond after cleavage…
CO2 is formed
electrophilic addition
electrophile attacks the bond
polymers
large molecule built by repetitive units of monomers
monomers
individual units of monomers
cellulose
polymer built of sugar monomers
proteins
polymers built from amino acid monomers
nucleic acids
polymer built from nucleotide monomers
polyalkenes
made from alkenes using a suitable polymerization catalyst
alkene polymerization
initiation, propagation (repeats), termination
vinyl monomers
many substituted ethylenes that yield polymers

propelyne= polypropylene

conjugated compounds
compounds that have alternating double and single bonds

HX bonds adds differently than Br2

conjugated compound + HX =
1, 2 addition
1, 4 addition
conjugated compound + Br2=
mixture
allylic carbocation
carbocation that is next to double bond

more stable than non-allylic carbocations

resonance hybrid of 2 forms

resonance

why are allylic carbocations more stable?
symmetrical
all 3 carbons are sp2 (1 pi 1 sigma)

each carbon has a vacant p orbital

resonance forms
two individual carbocation structures

<-->

don’t have to be equivalent

difference between resonance forms?
position of pi bond electrons/lone pairs
similarities between resonance forms?
atoms are in same place

atom connections

3d shape

resonance hybrid
allylic carbocation has single unchanging structure that is a blend all its resonance structures

characteristics of both structures= share bonds/charges equally

more stable than individual resonance forms

more resonance forms=
more stability

electrons spread over a larger part of molecule

resonance does not follow…
markovnikov’s rule
movement of lone pairs…
movement of charges
resonance forms follow…
octet rule
alkynes
hydrocarbons that contain C-C triple bonds

2 sp (1 sigma, 2 pi)

alkyne formula
CnH2n-2
alkyne suffix
-yne
enynes
compounds with both double and triple bonds
alkynes + 2 mol H2 + catalyst=
alkenes, then alkanes

can be stopped at alkene w/ lindlar catalyst

alkynes five cis alkenes when reduced because…
hydrogenation occurs with syn stereochemistry
vinylic halide
on the C=C
1 molar equivalent of HX yields…
vinylic halide
excess of HX yields…
dihalide product
bromine/chlorine + alkynes yields
dihalides
addition proceeds with…
stereochemistry (trans)
product of alkyn+ water
ketone
hydrated internal alkyne yields…
mixture of products
hydrated terminal alkyne yields…
one product

terminal alkynes are weakly acidic

acetylide anion–> terminal alkyne
terminal alkyne–> internal alkyne

acetylide anion
formed when strong bases like NaNH2 remove terminal hydrogens

react with alkyl halides via nucleophilic attack

aromatic
fragrant
benzene
C6H6

unsaturated

substitution reactions

planar, sp2, 120, perpendicular p orbitals

why is benzene less reactive than alkenes
resonance makes it more stable
acetophenone
benzene-
aryl group
represents a general aromatic ring
ortho-disubstituted benzene
1, 2 benzene
meta- disubstituted benzene
1, 3 benzene
para-disubstituted benzene
1, 4 benzene
phenol
-OH is at C1
toluene
-CH3 is at C1
electrophilic aromatic substitution
electrophile reacts with aromatic ring and substitutes from on the the hydrogen

most common aromatic compound reaction

less reactive towards electrophiles, needs catalyst

why does first step of electrophilic aromatic substitution have a high Eact?
allylic carbocation isn’t as stable as the original benzene ring

not as reactive to electrophiles

what does addition cause in aromatic rings?
resonance stability to be lost, need to substitute
alkylation
way to introduce alkyl groups onto benzene ring (Friedel-Crafts)
Friedel-Crafts alkylation reaction limitations
only halogens can be used unless its attached to a ring

NO2, CN, SO3H, COR make benzene less reactive

Friedel-Crafts acylation reaction
acyl group is introduced onto benzene ring
acyl group
R-C=O
activating groups
H, OH make benzene ring more reactive

donate e- to ring

make ring more e- rich

causes positive carbocation to be stable

Eact lowered, reaction quickened

deactivating groups
NO2, CHO, Cl make benzene ring less reactive

withdraw e- from ring

makes ring e- poor

makes pos carbocation more positive

raises Eact, slows reaction

-OH benzene orientation
para, ortho
-CN bezene orientation
meta
meta directing groups
deactivating

groups’ positively polarized atom is directly attached to ring

=O-C-R, O=C-R, C=-N, O-N=O

ortho, para directing groups
activating (excludes halogens)

lone pairs on atoms directly bonded to ring

OH, NH2, Cl, Br

how do halogens affect benzene orientation?
ortho-para

deactivating

inductive effet
withdrawal/donation of e- through a sigma bond

due to EN difference between ring’s groups

resonance effect
withdrawal/donation of e- through pi bond

due to p-orbital overlap between group and benzene ring

product distribution paralleles…
stability of intermediate
amino group with lone pairs…
ortho para mixture
what part of benzene ring reacts with KMnO4?
alkyl groups
benzylic position
place where KMnO4 attack the side chain of C-H bonds next to aromatic ring

radical intermediates

what are aromatic rings inert to?
reduction when under typical alkene hydrogenation conditions

needs high temp/pressure

KMnO4 unless it has alkyl groups

polycyclic aromatic compound
multiple benzene rings fused together
aromaticity
unusual behavior of cyclic conjugated molecules like benzene
heterocycles
aromatic compounds that contain atoms of two or more elements in their rings

6 pi e-

pyridine, pyrimidine, pyrrole, imidazole

pyridine and pyrimidine
1 pi e- on each of their ring’s atoms (hexagon)
pyrrole and imidazole
1 pi e- on each of the 4 atoms and 2 pi e-‘s on N-H (lone pair)

(pentagon)

reterosynthetic analysis
methodology of working backwards to devise a synthetic route
nitration of benzene+ HNO3/H2SO4=
NO2-benzene
sulfuration of benzene + SO3/H2SO4=
benzene-SO3H
friedel crafts catalyst
AlCl3
enol
alkyne intermediate

rarely isolated

product of alkyne hydration?
ketone
phenyl group
C6H5-
benzyl group
C6H5CH2-
arylamine
ArNH2
which ortho/para resonance structure is most stable?
lone pairs on oxygen

more bonds

which meta directing ortho/para structure is least stable?
one with + closest to the C because this creates too much strain
x

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