CHE 331 final

organic acids (2 kinds)

acids with an H bonded to an electronegative atom such as O, or acids bonded to a carbon atom that is adjacent to a strong EWG (such as a carbonyl group)

5 factors that determine acidity

1. charge (positive is more acidic)

2. electronegativity (more electronegative = more acidic)

3. s-character (sp is more acidic then sp3)

4. delocalization (more resonance is more acidic)

5. inductive effect (EWG stabilize negative charge, more acidic)

constitutional isomers

have different structural formulas

conformational isomers

result from bond rotation

newman projections stability of 4 types

staggered is most stable, eclipsed is least stable. anti confirmation (staggered) has the two methyls as far as possible and is most stable. gauche conformation has the two methyls 60 degrees apart and is unstable.

stereoisomers

atoms are connected in the same way but differ in 3d orientation. ex cis trans

angle strain

strain due to expansion/compression of ideal 109.5 bond angles. mostly in 3 or 4 membered rings

torsional strain

strain due to eclipsing bonds between neighboring atoms (eclipsed conformation)

steric strain

strain due to repulsive interactions when atoms approach each other too closely (ex. gauche interactions)

conformations of cyclohexane

chair conformation has no angle or torsional strain, most stable. twist boat conformation is free of angle strain but has steric and torsional strain

positions for substituent in a chair conformation

axial - point up or down equatorial - fan out diagonally. more stable due to less 1,3-diaxial interactions

ring flips

move each carbon by one spot.

naming polycyclic molecules

Xcyclo[Y,Y,Y]Zane where X is the number of rings, Y is the number of carbons in each bridge, and X is the total number of carbons

enantiomers

non-superimposable mirror images. all chiral centers are flipped

achiral

has a plane of symmetry. superimposable with its mirror image

R and S configuration

if the highest priority group is wedged, a clockwise arrow is R, and a counterclockwise arrow is S. otherwise its the opposite

# of possible stereoisomers

a molecule with n chirality centers can have up to 2^n stereoisomers (may have fewer)

diastereomers

not mirror images. only have flipped stereochemistry at some chirality centers. can be cis-trans diastereomers or configurational diastereomers

meso compounds

achiral but contain chirality centers

racemic mixture

50:50 ratio mixture of S and R enantiomers. shows no optical rotation

prochiral

can be converted from achiral to chiral in a single chemical step

polarizability

measure of how easily an atoms electron cloud can be distorted by an external electric field

nucelophile

negatively polarized, electron-rich atom (ex. base)

electrophile

positively polarized, electron-poor atom (ex. atom)

exothermic and endothermic reactions

in exothermic reactions, the products have stable bonds and the reactants have weaker bonds. the opposite is true for endothermic reactions.

degree of unsaturation

( 2C + 2 + N - H - X ) /2

ignore any oxygens

alkene nomenclature

start numbering the end closer to the double bond. cycloalkenes are named so that the double bond is between C1 and C2 and the first substituent has as low of a number as possible

E/Z isomers

used for stereochemistry of double-bond alkenes beyond disubstituted alkenes. ranked based on highest priority group. Z is Zame Zide and E is opposite sides.

cis and trans isomer stability

trans isomers are more stable due to less steric strain. the more substituents present on the double bond, the more hyper conjugation, and the more stable the alkene.

hyperconjugation

the stabilizing interaction between C=C pi orbitals and the adjacent C-H sigma bonds on substituents

markovnikov's rule

says that in the addition of HX to an alkene, the H attaches to the less substituted carbon and the X to the more substituted carbon

carbocations

planar and triangular. tertiary are most stable and primary are least stable, due to inductive effect and hyperconjugation. a more stable intermediate forms more quickly then a less stable intermediate.

hammond postulate

the structure of the transition state resembles the structure of the species it is closest to in energy (the species with the higher energy and less stability). transition states for endothermic reactions resemble products, and transition states for exothermic reactions resemble reactants.

hydride shift

shift of a hydrogen atom and its electron from one carbon to a neighboring carbon

addition of Br2/Cl2, CCl4 to alkenes

yields 1,2-dihalides. anti addition. only trans isomer is formed on a cycloalkene. a positively charged, three-membered ring is formed (bromonium/chloronium ion). The second X attacks via an SN2 mechanism.

addition of Br2/Cl2, ROH to alkenes

forms a 1,2-haloalcohol. anti addition and mark addition (OH attacks more substituted). forms a bromonium/chloronium ion and then the OH attacks the more electrophilic/more substituted carbon

addition of 1. Hg(OAc)2, ROH, 2. NaBH4 to alkenes

forms a C-OR. mark addition (for OH) with anti stereochem. first step forms a bridged three-membered mercurinium and OH attacks more substituted carbon. second step is radical reduction

addition of H2O in H3O+ to alkenes

forms an alcohol. mark addition with mixed stereochem. first, the alkene attacks a proton to form a carbocation. carbocation rearrangements can occur.

addition of HX to alkenes

forms an alkyl halide. mark addition with mixed stereochem. first, the alkene attacks a proton to form a carbocation. carbocation rearrangements can occur.

addition of HBr, ROOR, Δ to alkenes

forms an alkyl bromide. anti-mark addition with mixed stereochem. radical mechanism, with radical Br adding to the alkene first.

addition of 1. OsO4, 2. NaHSO3 / H2O to alkenes

forms a vicinal diol. syn addition.

addition of 1. mCPBA, 2. NaOH or H3O+ to alkenes

forms a vicinal diol. anti addition. epoxide intermediate that is opened up by hydroxide.

addition of mCPBA to alkenes

forms an epoxide. syn addition.

addition of 1. BH3·THF, 2. H2O2, NaOH to alkenes

forms an alcohol. anti-mark addition with syn stereochem.

addition of D2 or H2, Pd/C to alkenes

forms an alkane. syn addition.

addition of CH2I2, Zn/Cu to alkenes

forms a cyclopropane. syn addition.

addition of CHCl3, KOtBu to alkenes

forms a dichlorocyclopropane. syn addition. KOtBu emoves a proton from chloroform, causing the elimination of a chloride ion. This generates dichlorocarbene (:CCl2), a highly reactive electrophile.

addition of KMnO4, H3O+ to alkenes

can form ketones and carboxylic acids. disubstituted alkene carbons become ketones. monosubstituted alkene carbons become carboxylic acids.

addition of 1. O3, 2. Me2S or 1. OsO4, 2. NaIO4 to alkenes

can form ketones and aldehydes. no carboxylic acid is formed.

addition of D2 /H2, Pd/C to alkynes

forms an alkane. syn addition.

addition of H2, Lindlar's Catalyst to alkynes

cis alkene. syn addition. "poisoned" catalyst

addition of Li NH3 to alkynes

trans alkene. anti addition

addition of 1. BH3 THF, 2. H2O2,NaOH to alkynes

forms an enol (C=C(OH)) that undergoes tautomerization to become a ketone (internal alkynes) or an aldehyde (terminal alkynes). anti-mark addition with syn stereochem.

addition of H2O,H3O+ to alkynes

forms an enol, which tautomerizes to a ketone. mark addition with mixed stereochem. a vinyllic carbocation is formed and attacked by water to form an enol.

addition of HX to alkynes

forms a vinyllic halide or a dihalide (if HX is in excess). mark addition with anti stereochem.

addition of HBr, ROOR, Δ to alkynes

forms a vinyllic bromide. anti mark addition with mixed stereochem. free radical chain mechanism

addition of X2,CCl4 to alkynes

forms a 1,2-dihaloalkene. anti addition. forms a bromonium ion intermediate.

addition of X2,ROH to alkynes

forms a α-halo ketone via an enol intermediate. mark addition (for OH). anti addition with syn stereochem. forms a bridged bromonium/chromium ion intermediate.

addition of 1. Hg(OAc)2,ROH, 2. NaBD4 to alkynes

forms an enol ether, mark addition with anti stereochem. forms a bridged mercurinium ion intermediate and the OH attacks the more substituted carbon.

addition of 1. OsO4, 2. NaHSO3/H2O to alkynes

1,2-diketone. syn addition

deshielding effect on NMR

the more deshielded the nuclei are, the further downstream they are. the more shielded, the further upstream

splitting in NMR

protons that have n equivalent neighbors (in the same environment) show n+1 peaks

partial charges in a carbon halogen bond

halogen has a partial positive while carbon has a partial negative

3 steps of radical reactions

initiation- homolytic cleavage of a molecule. propagation- a radical attacks a stable molecule termination- two radicals come together. never part of a mechanism

hydrogens that re easiest to pull off in a radical reaction

tertiary or conjugated stabilized Hs

selectivity of Cl2 and Br2 radical reactions

Br2 is more selective, favors formation at more substituted radical position. Cl2 has no selectivity (Cl radicals are more reactive)

NBS

substituted a hydrogen atom with a bromine atom at the allylic position. avoids turning an alkene into a dibromide. major product is determined by looking first at the stability of the radical, and second at the stability of the alkene.

most stable radicals

allylic and benzyllic

SOCl2/PBr3

convert primary and secondary alcohols into alkyl chlorides/bromides. substitution (SN2) and invert stereochemistry. make OH into a good leaving group

gringard reagents

formed by reacting alkyl bromides with Mg. can react with Li for synthesis

SN2 reactions

second order reactions. concerted reaction, nucleophile performs a backside attack the causes the leaving group to leave.

steric effects in SN2

SN2 reactions happen only at unhindered carbons (mostly with primary or sometimes secondary halides). can't happen for vinyllic or aromatic carbons. epoxides can undergo SN2. an adjacent quartenary group can also prevent SN2

good nucleophiles

the more basic, the more nucleophilic.

good leaving groups

stabilize the negative charge in the transition state best. these are weak bases such as Cl-, Br-, TsO-. poor leaving groups are OH-, Or-, H2N-.

protic solvents

contain an -OH or -NH group. good for SN1/E1 reactions (solvate the carbocation intermediate and the leaving group)

polar aprotic solvents

polar and don't have an -Oh or -NH group. best for SN2 reactions (don't solvate). DMSO, DMF, CH3CN

SN1 reactions

first order. the rate-determining step is the spontaneous dissociation of the leaving group. forms a carbocation, can have carbocation rearrangements, stereochemistry is lost. result is a racemic mixture. the first step is highly reversible. rate is not affected by the nucelophile

substrates in SN1

the more stable (tertiary, secondary) the substrate, the faster the SN1 reaction

zaitsev's rule

more stable (substituted) alkene is preferred during elimination reactions

E1 reactions

the C-X bond breaks first to give a carbocation intermediate, which abstracts an H+ to give an alkene. gives more stable product based on zaitsev's rule.

E2 reactions

concerted reaction. the H+ is abstracted at the same time as the C-X bond is broken, alkene is formed in one step. happen when an alkyl halide is traded with a strong base. periplanar geometry is needed for the reaction (H and X have to be trans diaxial)

E1cB reaction

base-induced cleavage of the C-H bond happens first, which gives a carbanion intermediate. the anion is the conjugate base of the acid reactant, and loses the X to give the alkene. happens in reactions with a poor leaving group such as OH-, or mostly reactions where the leaving group is 2 carbons away from a carbonyl group (so that the hydrogen is extremely acidic)

reason for stability of conjugated dienes

in normal C-C bonds, the bond is formed from overlap of sp3 orbits. in conjugated dienes, the bond is formed by sigma overlap of sp2 orbitals (which have more s character)

what atoms can contribute to conjugation

only sp or sp2 atoms (radicals, carbocations, carbanions). sp3 cannot participate

of nodes in MO

orbital # - 1

1,2 product vs 1,4 product

the 1,2 product is the kinetic product that is formed faster (favored at low temps). 1,4 is the thermodynamic product that is rearranged to give a more stable product (favored at high temps). the more stable carbocation forms, then there is resonance to from the more stable alkene

endo product

most favored product (happens faster, even though exo product is more stable). trans group has the same stereochemistry as the EWG. not necessary in intramolecular diels-alder.

reactions of dienes

negative side (side with EWG on dienophile) has to line up with positive side (side with EDG on diene). diene must form into a cis conformation in order to react, and its better when the methyls on C1 and C4 are trans

UV absorption of conjugated compounds

gaps between the HOMO and LUMo absorb UV light. more conjugation (longer uninterrupted chain) = smaller gap = longer wavelength absorbed = less energy needed to excite the electron

base peak and molecular ion (parent) peak

the base peak is the tallest peak, most common cation. the M+ peak is the unfragmented cation (gives the molecular weight)

alcohol fragmentation

alpha cleavage or dehydration (become alkenes). give a peak 18 amu from from M+ peak

amine fragmentation

odd number M+, alpha cleavage

halide fragmentation

Br has a 1:1 ratio of M+ and M+2 (79:81). Cl has a 3:1 ratio of M+ and M+2 (35:37)

carbonyl fragmentation

alpha cleavage or mcLafferty rearrangement (ketones and aldehydes that have an H 3 carbons away from carbonyl)

benzene fragmentation

usually gives a peak at 77 amu

absorption of IR light

absorbed by covalent bonds in molecules with a dipole moment. a stronger chemical bond vibrates at a higher frequency. a bond between heavier elements vibrates at a lower frequency

common IR stretches

carbonyls appear as a sword, carboxylic acids appear as a beard, alcohols appear as a tongue

arene nomenclature

if the alkyl substituent on the benzene ring is smaller (less carbons) then the ring, it is named as a benzene ring with an attachment. if the substituent on the ring is larger, it is named as an alkane with a benzene attachment

ortho, meta, para

ortho (1,2) meta (1,3) para (1,4)

length of benzene bond

intermediate between the length of a single and double bond. all carbons are sp2 hybridized and the molecule exists between two resonance forms