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CHEM 2211: Final Exam
Sp3 |
4 single bonds
109.5
3 2p orbitals combined with 2S orbital |
Sp2 |
1 double bond
120
1 2S combined with 2 2P forming 3 SP2 and 1P unchanged |
SP |
triple bond
180
1 2S overlaps 1 2P= 2 SP orbitals 2 P unchanged |
Formal Charge |
FC= (# valence e) - (# of bonded e)/2 - (# non bonding e) |
Bronsted lowry |
acid= donates H+--- forms conjugate base
base= accepts H+ --- forms conjugate acid
|
PKa |
Pka= -logKa
strong acid= small Pka
Strong base= large PKa
Ka= [products]/ [reactants] |
lewis acid/ base |
acids= accept e
- low energy orbitall or polar bond to H
- metal cations/ halogen acids/ 3 compounds/ transition metals
base= donates e or pair of non bonding e
- most contain O or N |
dipole-dipole interaction |
between polar molecules |
dispersion forces |
constantly changing electron distribution
van der wall force |
hydrogen bond |
H- EN
hydrophillic |
ant-conformation |
180 apart |
gauche |
60 apart
3.85 KJ more than anti
- due to steric strain= atoms forced closer together
|
eclipsed |
highest energy/ least stable
12 KJ more than gauche
-torisonal strain
-C-H = 4.0 KJ |
ortho |
2 substituents on adjacent carbons on a benzene ring |
aromatic rings |
assume all are planar
4n + 2 = pi electrons |
weak acids |
large Pka value
OCH3 group contributes EN to ring= weak acid |
heat of combustion |
amount of heat released when a compound is burned in O2
higher the strain= higher the heat of combustion |
specific rotation |
SR= observed rotation/ pathlength x concentration |
chiral |
not superimposable mirror image
no plane of symmetry |
enantiomer |
mirror images- not superimposable
light cancels out |
# of sterioisomers |
1 chiral center= 2
2 chiral centers= 4
3 chiral centers= 6 |
meso compounds |
2 chiral centers
line of symmetry
not optically active
|
racemic mixture |
50:50 mixture of 2 enatiomers
0 optical rotation |
racemic mixture |
... |
prochirality |
if a molecule can be converted from achiral to chiral in single chemical step |
exothermic |
bonds formed are stronger than bonds broken
releases energy to surroundings |
degree of unsaturation |
# of bonds/ rings a molecule has
CnH2n+2
subtract 1 for every N
ignore O |
alkene |
no free rotation around double bonds
350KJ to break |
hygrogenation |
larger heat of hydration= higher energy= less stable |
hydrolysis |
degradation of substance in water |
dehydrohalogenation |
alkyl halide + strong base (KOH)---- loss of HX-- forms alkene
- elimination |
dehydration |
alcohol + strong acid (H2SO4)--- alkene |
polar reaction |
unsymmetrical bond breaking and forming
- between compounds w/ even number of electrons
- most common type of reaction
- 1 element keeps the pair of electrons
-heterolytic
- electron rich sites react with electron poor sites |
radical reactions |
symmetrical bond breaking and making
- 1 electron remains with each element
- homlytic
- take place in gas phase |
Keq |
equilibrium constant that shows the rate of products to reactants
- [products] / [reactants]
- K > 1= product concentration > reactant concentration
- K = 1 = fair amount of both
- K < 1 = reactant > product---- does not appear as written; in reverse |
favorable reactions |
exergonic:
- favorable
G= -RT ln Keq
R= 8.314
T= kelvin |
bond dissociation energy |
measures heat needed to break a bond
exothermic= bonds formed are stronger than bonds broken |
stability of alkenes |
cis alkenes are less stable than trans b/c of steric strain
stability determined by:
-cis trans equilibrium constants= product favored= more stable
- hydrogenattion= treatment of alkene w/ H2
---- more energy released= less stable
- more subs on double bond= more stable= stronger sp2-sp3 bonds |
carbocation |
planar
increase with substitution |
the hammond postulate |
the transition state resembles reactants or products= which ever closer in energy to
exergonic resembles reactants
endergonic transition state resembles products |
substitution vs elimation |
major product:
-sub= if leaving group is on primary
-elimination= if leaving group is on tertairy
Strong base: -OH Poor nuc: H2O or RHO
1= Sn2 favored 1= no reaction
2= mostly E2 2= Sn1/ E1 in polar protic solvents
3= E2 3= Sn1/ E1 in polar protic solvents
weak base: Cl
1= Sn2
2= mostly Sn2
3= SN1/ E1 in polar protic solvents |
Sn2 |
rate depends on alkyl halide and leaving group
single step= no intermediates
attaches at opposite side
favors:
-small methyl/ primary molecules
- vinylic and aryl halides are unreactive
leaving group:
F<Cl<Br<I < TosO
aprotic solvents:
CH3OH< H2O< DMSO<DMF<CH3CN< HMPA |
nucleophile |
electron rich
negative nuc= neutral product
neutral nuc= positive product
nuc increases going down periodic table |
Sn1 |
2 steps= intermdiate
unimolecular
produces racemic mixture
polar protic solvents
- -OH or -NH
favors tertairy
weak nucleophile= H2O RHO |
E2 |
Strong base
-tertiary/ secondary
primary=sn2 |
Sn2 |
strong nucleophile/ base
primary
weak base- Cl
primary/ secondary |
O-H/ N-H |
3400 |
C-H Sp3 |
2800-3000 |
C-H Sp2 |
3000-3100 |
C-H Sp |
3300 |
alkyne/ nitrile |
2100 |
C=O |
1700 |
C=C |
1600 |
aromatic |
1500 |
oxidation |
increases O content/ decreases H content
CrO3, K2Cr2O7, K2CrO4, Hot KMnO4
potent oxidizers
chromium under acidic conditions
KMnO4= basic conditions
alkenes/ alkynes/ alkylbenzenes= cleavage product
HIO4=vicinal diol= OH attached to adjacent carbons |
Reduction |
loss of O content
Carbonyl= Metal Hydrids
alkenes= hydrogenation
alkynes= hydrogenation or metal in NH3 |
diels-Alder reaction |
in heat
Diene + Alkene---- cyclohexene
stereospecific
syn addition= same side
endo forms major project= subs opp of chair |