CHEM 2211: Final Exam
57 Cards in this Set
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Sp3
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4 single bonds
109.5
3 2p orbitals combined with 2S orbital
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Sp2
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1 double bond
120
1 2S combined with 2 2P forming 3 SP2 and 1P unchanged
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SP
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triple bond
180
1 2S overlaps 1 2P= 2 SP orbitals 2 P unchanged
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Formal Charge
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FC= (# valence e) - (# of bonded e)/2 - (# non bonding e)
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Bronsted lowry
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acid= donates H+--- forms conjugate base
base= accepts H+ --- forms conjugate acid
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PKa
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Pka= -logKa
strong acid= small Pka
Strong base= large PKa
Ka= [products]/ [reactants]
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lewis acid/ base
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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
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dipole-dipole interaction
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between polar molecules
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dispersion forces
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constantly changing electron distribution
van der wall force
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hydrogen bond
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H- EN
hydrophillic
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ant-conformation
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180 apart
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gauche
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60 apart
3.85 KJ more than anti
- due to steric strain= atoms forced closer together
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eclipsed
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highest energy/ least stable
12 KJ more than gauche
-torisonal strain
-C-H = 4.0 KJ
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ortho
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2 substituents on adjacent carbons on a benzene ring
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aromatic rings
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assume all are planar
4n + 2 = pi electrons
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weak acids
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large Pka value
OCH3 group contributes EN to ring= weak acid
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heat of combustion
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amount of heat released when a compound is burned in O2
higher the strain= higher the heat of combustion
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specific rotation
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SR= observed rotation/ pathlength x concentration
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chiral
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not superimposable mirror image
no plane of symmetry
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enantiomer
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mirror images- not superimposable
light cancels out
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# of sterioisomers
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1 chiral center= 2
2 chiral centers= 4
3 chiral centers= 6
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meso compounds
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2 chiral centers
line of symmetry
not optically active
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racemic mixture
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50:50 mixture of 2 enatiomers
0 optical rotation
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racemic mixture
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...
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prochirality
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if a molecule can be converted from achiral to chiral in single chemical step
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exothermic
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bonds formed are stronger than bonds broken
releases energy to surroundings
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degree of unsaturation
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# of bonds/ rings a molecule has
CnH2n+2
subtract 1 for every N
ignore O
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alkene
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no free rotation around double bonds
350KJ to break
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hygrogenation
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larger heat of hydration= higher energy= less stable
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hydrolysis
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degradation of substance in water
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dehydrohalogenation
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alkyl halide + strong base (KOH)---- loss of HX-- forms alkene
- elimination
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dehydration
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alcohol + strong acid (H2SO4)--- alkene
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polar reaction
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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
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radical reactions
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symmetrical bond breaking and making
- 1 electron remains with each element
- homlytic
- take place in gas phase
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Keq
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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
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favorable reactions
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exergonic:
- favorable
G= -RT ln Keq
R= 8.314
T= kelvin
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bond dissociation energy
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measures heat needed to break a bond
exothermic= bonds formed are stronger than bonds broken
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stability of alkenes
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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…
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carbocation
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planar
increase with substitution
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the hammond postulate
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the transition state resembles reactants or products= which ever closer in energy to
exergonic resembles reactants
endergonic transition state resembles products
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substitution vs elimation
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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
…
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Sn2
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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
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nucleophile
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electron rich
negative nuc= neutral product
neutral nuc= positive product
nuc increases going down periodic table
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Sn1
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2 steps= intermdiate
unimolecular
produces racemic mixture
polar protic solvents
- -OH or -NH
favors tertairy
weak nucleophile= H2O RHO
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E2
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Strong base
-tertiary/ secondary
primary=sn2
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Sn2
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strong nucleophile/ base
primary
weak base- Cl
primary/ secondary
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O-H/ N-H
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3400
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C-H Sp3
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2800-3000
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C-H Sp2
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3000-3100
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C-H Sp
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3300
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alkyne/ nitrile
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2100
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C=O
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1700
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C=C
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1600
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aromatic
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1500
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oxidation
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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
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Reduction
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loss of O content
Carbonyl= Metal Hydrids
alkenes= hydrogenation
alkynes= hydrogenation or metal in NH3
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diels-Alder reaction
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in heat
Diene + Alkene---- cyclohexene
stereospecific
syn addition= same side
endo forms major project= subs opp of chair
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CHEM 2211: Study Guide