CHEM 238

What factors would favor an SN1 over SN2

SN1 - tertiary halides, weak nucleophiles, protic solvent
SN2 - primary halides, strong nucs, aprotic solvent

What factors would favor E1 vs E2

E1 - tertiary halide, weak base
E2 - strong base

What factors would favor an SN2 vs E2

SN2 - tertiary nucleophile, not tertiary
E2 - strong base

What factors would favor an SN1 vs E1

these will almost always show up together

What factors influence stability of radical

more crowded radicals are more stable; resonance also helps

Compare and contrast reaction of alkene and HBr with or without peroxides

alkene and HBr - gives more crowded product and may show cation shifts
peroxides - gives less crowded product, no shifts

what makes acetylide ions useful for organic synthesis

relatively easy to form and will make new C-C bonds

how can alcohol be converted into strong electrophile, strong nucleophile, and good leaving group (originally bad at all of those)

strong electrophile - protonate it (w/ strong acid)
strong nucleophile - deprotonate it (w/ strong base)

good leaving group - protonate it (w/ strong acid)

compare and contrast how strong and weak oxidants react with primary and secondary alcohols

primary and strong - carboxylic acid
primary and weak - aldehyde
secondary and any oxidant - ketone

why are epoxides substantially more reactive than other ethers

the 3 membered ring is unstable due to ring strain and it is favorable to relieve it

compare and contrast reaction of epoxides under acidic or basic conditions (regiochem and stereochem)

both lead to trans product (attacks from behind epoxide)
basic attacks less crowded carbon and acidic attacks more crowded carbon

why are ethers and sulfides so much less reactive than alcohols and thiols

they don’t have OH/SH which knocks out acidity, relatively less polar as they are closer to being symmetric

what general information do we get from NMR, IR, and MS

MS - MW/formula
IR - bonds/functional groups
NMR - number and types of C and H, specific structure

what do integration, chem shift, number of peaks, and splitting tell us in an NMR spectrum

number of peaks - how many types of Hs
integration - relative number of Hs in a type
chem shift - what environment is each type of H

splitting - how many neighboring H’s are there

How does an IR tell us about the presence or absence of C=O, O-H, and N-H

C=O - strong peak around 1700
OH or NH - broad peak around 3200-3500

Describe relative stability of different dienes

conjugated dienes (ex. 1,3) are most stable
cumulated dienes (double bonds right next to each other, 1,2) are least stable

isolated (further apart) are in the middle

What do we determine the kinetic and thermo products of a diene reacting with HX

kinetic - dominates at low temp, will be 1,2 addition
thermo - dominates at high temp, will be most stable product (most crowded alkene usually)

What determines if a compound will be aromatic, nonaromatic, or antiaromatic

nonaromatic - not planar, fully conjugated ring
anti - 4N pi electrons
aromatic - 4n+2pi electrons

compare and contrast reactions of benzene vs cyclohexane

benzene does substitutions that maintain benzene pi core, cyclohexene does additions that consume pi bond; both cases - pi bond is nucleophile

compare and contrast following reactions: nitration, sulfonation, halogenation, Friedel-crafts alkylation, fridel-crafts acylation

all follow same standard mechanism where benzene is a nucleophile and attacks an electrophile; difference is what functional group of the product is
Friedel crafts is also way to add C-C bonds (w/ acylation there is always ketone)

what determines whether benzene derivative will be more or less reactive than benzene

more reactive - carbocation intermediate is stabilized by an EDG substituent - either alkyl group or group that has lone pair
less reactive - carbocation intermediate is destabilized by an EWG substituent - usually it has a pi bond; halogens also count

EDGs push electron density into the benzene ring.

Effects

• Activate the ring → makes it more reactive toward electrophiles
  EWGs pull electron density away from the benzene ring.

  Effects

  • Deactivate the ring → makes it less reactive toward electrophiles

what determines whether a benzene derivative will be an ortho/para director or a meta director

O/P - intermediate carbocations are stabilized by the substituent (includes all activators and halogens)
Meta - o/p intermediate carbocations are destabilized by the substituent (deactivators except halogens)

why are allylic and benzylic anions, cations, and radicals more stable than their alkyl counterparts

have additional resonance stabilization (allylic - adjacent C=C pi bond, benzylic - aromatic pi system of benzene)
Allylic and benzylic species are more stable because:

1. The charged/radical carbon has a p orbital.

2. It overlaps with an adjacent π system (C=C or benzene ring).

3. Electrons can delocalize through resonance.

4. The charge or radical is spread over multiple atoms, lowering energy.

describe isoprene units found in DMAP and IPP

5 carbon, 2-methylbutane chain that may or may not have pi bonds or a leaving group. 1 molecule of DMAP reacts with 1 molecule of IPP to form a 10 carbon unit. This can cyclize or react with more DMAP to continue growing

compare and contrast the reactivity of vinyl and aryl halides with alkyl halides

vinyl and aryl halides don’t do any standard substitution/elimination chemistry with 2 exceptions. Highly activated (with EWG groups) aryl halides can do nucleophilic aromatic substitution. Vinyl halides can do E2 reactions to form alkynes

reactions from ch 12: ethers, epoxides, and glycols

williamson ether synthesis (SN2 reaction between deprotonated alc using NaH and non-tertiary halide), ether cleavage (occurs using HX and heat, where SN1 generally dominants over SN2, epoxide synthesis (mcpba or intramolecular cyclization of halohydrins), epoxide ring opening, grignard/barbier reagents (formed from C-halogen bonds and highly water sensitive), glycols (cis formed from alkenes using KMnO4/H2O/OH- or OsO4, trans prepared via epoxide route)

reactions from chapter 11: alcohols and thiols

dehydration (using acids like H2SO4 or H3PO4 - E1 dominates over E2, tertiary and secondary work best as primary generally do not react), synthesis of alkyl halids (HX reactions - SN1 dominates due to protic environment and works best for secondary/tertiary alcs; Magic reagents - SOCl2 or PBr3 for primary or secondary alc via SN2-adjacent mechanism), Sulfonate ester reactions (good LGs), Oxidation (strong, weak, and thiols oxidized by Br2 or I2 to form disulfides), alc synthesis from alkenes (hydroboration for less sub, oxymercuration for more sub)