Organic Chemistry: SN1/SN2, Reactions, and Spectroscopy

Which mechanism is faster?

SN2 is faster on primary/secondary, SN1 faster on tertiary

When do you use SN1 vs SN2?

SN1: tertiary, weak nucleophile; SN2: primary/secondary, strong nucleophile

Stereochemistry of SN1 vs SN2?

SN1: racemic mixture; SN2: inversion

How to predict substitution of haloalkanes?

Primary → SN2, Tertiary → SN1

Alkanes vs alkenes reactivity?

Alkanes: substitution; Alkenes: addition

How to predict alkene reactions?

Look for C=C, do addition (H2, HX, X2, H2O)

Markovnikov's rule?

H adds to carbon with more Hs, X adds to carbon with fewer Hs

Electrophile for benzene reactions?

Positively charged species, e.g., NO2⁺

Role of H2SO4 in nitration?

Generates NO2⁺ from HNO3

Predict solubility in water?

More H-bonds = more soluble; longer hydrocarbon = less soluble

Compare boiling points?

Stronger intermolecular forces = higher BP; carboxylic acid > alcohol > ketone/aldehyde > alkane

IR peaks for functional groups?

OH 3200-3600, C=O ~1700, C=C ~1600, N-H ~3300

NMR splitting?

n+1 rule

Identify chiral carbon?

Carbon with 4 different groups

What are enantiomers?

Mirror-image stereoisomers, rotate plane-polarized light opposite

Racemic mixture?

50:50 enantiomers, no rotation

Alkanes + halogens?

Substitution via free radicals (UV)

Homolytic vs heterolytic fission?

Homolytic: radicals; Heterolytic: ions

Catalyst for hydrogenation?

Ni or Pt

Reducing agents?

H2/Ni: alkene→alkane,
NaBH4: aldehyde/ketone→alcohol, "
LiAlH4: aldehyde/ketone/carboxylic acid/ester→alcohol

Oxidation of alcohols?

Primary → aldehyde → acid,
Secondary → ketone,
Tertiary → none

IR + NMR to identify functional groups?

Look for characteristic peaks and splitting patterns

Alcohol/alkane naming basics?

Longest chain + functional group suffix; number for lowest locant

Ester formation?

Alcohol + carboxylic acid + H2SO4 → ester + water

Identify polymer?

Repeating monomer units; addition: alkene opens, condensation: di-functional monomers

Hydrogen bonding?

O-H or N-H groups only

Haloalkane + NaOH?

Alcohol formation;
Primary → SN2,
Tertiary → SN1

Predict ¹H NMR signals?

Count distinct hydrogen environments

Least soluble alcohol?

Longest nonpolar chain

Cis vs trans?

cis: same side
trans: opposite side

Generate NO2⁺?

H2SO4 + HNO3

Primary, secondary, tertiary alcohol?

Primary: -OH on 1° carbon,
Secondary: -OH on 2° carbon,
Tertiary: -OH on 3° carbon

Reduce ketone?

Secondary alcohol (NaBH4)

Reduce carboxylic acid?

Primary alcohol (LiAlH4)

Electrophilic addition products of alkenes?

Add H-X, X2, or H2O across double bond, follow Markovnikov

Identify amide?

C=O bonded to NH2; -CONH2

Haloalkane + NH3?

Forms amine; excess NH3 prevents multiple substitutions

Identify compounds causing body odor?

Often carboxylic acids

K2Cr2O7 oxidation color change?

Orange → green for primary/secondary alcohols

no change for tertiary

Racemic mixture formation?

Chiral center formed via SN1 or planar intermediate

Addition vs substitution?

Alkene → addition; Alkane → substitution (UV + halogen)

Ester vs ether?

Ester COOC

Ether COC

Haloalkane SN1/SN2 rate?

Tertiary faster SN1;
Primary faster SN2;
Secondary depends

Alcohol oxidation type?

Primary → aldehyde → carboxylic acid

Secondary → ketone;
Tertiary → none

Reflux vs simple heating?

Reflux prevents loss of volatile compounds; simple heating may lose reactants

Distillation?

Separate liquids by boiling points

Electrophile vs nucleophile?

Electrophile: electron-deficient, Nucleophile: electron-rich

Good nucleophile?

Negative charge, less hindered

Boyle’s Law

(P₁)(V₁)=(P₂)(V₂)

Ideal Gas Law?

PV=nRT

Combined Gas Law?

P₁V₁/T₁=P₂V₂/T₂

Molarity?

M = moles/L

Dilution formula?

M₁V₁=M₂V₂

Stoichiometry steps?

Balance, convert grams ↔ moles ↔ liters

Limiting reagent?

Reactant that runs out first, determines product

Percent yield?

(Actual/Theoretical)×100

Solubility trends?

Polar dissolves polar; H-bonding increases solubility

Analytical techniques: IR?

Functional groups, bond type

¹H NMR?

Hydrogen environment, splitting, integration

Mass spectrometry?

Molecular mass, isotope pattern

Reflux?

Heat reaction without losing volatile compounds

Electrophilic substitution: benzene?

Electrophile attacks, sigma complex forms, H⁺ leaves, aromaticity restored

Which alcohols oxidize?

Primary & secondary;
tertiary do not

Which alcohol forms carboxylic acid?

Primary alcohol under excess oxidant

Which alcohol forms ketone?

Secondary alcohol

Why tertiary alcohols resist oxidation?

No H on carbon with -OH

Which compounds show single ¹H NMR peak?

Molecules with all hydrogens equivalent

Effect of chain length on solubility?

Longer nonpolar chain = less soluble

Effect of branching on boiling point?

More branching → lower

Which functional groups have strong H-bonding?

Alcohols, amines, carboxylic acids

Which functional groups are planar?

C=O, C=C, aromatic rings

Alkanes

Only single bonds, low reactivity, substitution reactions with UV

Alkenes

Contain C=C, undergo addition reactions

Alkane combustion

Complete: CO₂ + H₂O, Incomplete: CO or C (soot)

Free radical halogenation

Requires UV, involves initiation, propagation, termination

Initiation

X₂ → 2 X· (homolytic fission)

Propagation

X· + RH → R· + HX; R· + X₂ → RX + X·

Termination

Radicals combine to form stable molecules

Hydrogenation of alkenes

Alkene + H₂ → Alkane, catalyst Ni or Pt

Halogenation of alkenes

Alkene + Br₂ → dibromoalkane, Br₂ (aq) loses color

Hydration of alkenes

Alkene + H₂O → Alcohol (acid catalyst)

Addition of hydrogen halides

Alkene + HBr/HCl → Haloalkane, Markovnikov's rule

SN2

One-step, backside attack, primary carbons, inversion, strong nucleophile

SN1

Two-step, carbocation intermediate, tertiary carbons, weak nucleophile OK, racemic mixture

Haloalkanes + NaOH

Alcohol (Primary → SN2, Tertiary → SN1)

Haloalkanes + NH3

Amines, excess NH3 prevents multiple substitution

Alcohol oxidation

Primary: aldehyde → carboxylic acid, Secondary: ketone, Tertiary: no reaction

Esterification

Carboxylic acid + Alcohol ⇌ Ester + Water, H2SO4 catalyst

Esters

Fragrance or flavoring

Reducing agents

H2/Ni: Alkene → Alkane; NaBH4: Aldehyde/Ketone → Alcohol; LiAlH4: Aldehyde/Ketone/Carboxylic acid/Ester → Alcohol

Chiral carbon

Carbon with 4 different groups

Enantiomers

Mirror images, rotate plane-polarized light opposite

Racemic mixture

50:50 mixture, no rotation

Cis/trans in cyclic compounds

cis = same side, trans = opposite side

Neighboring members of homologous series

Differ by CH₂

Boiling points

Carboxylic acid > Alcohol > Aldehyde/Ketone > Alkane

Solubility

More H-bonding → more soluble, longer hydrocarbon → less soluble

IR spectroscopy

OH 3200-3600, C=O ~1700, C=C ~1600

Mass spectrometry

M⁺ peak = molecular mass; Br: M & M+2 equal; Cl: 3:1 ratio

Functional groups

Alkane -ane, Alkene -ene, Alcohol -ol, Haloalkane chloro/bromo/iodo, Aldehyde -al, Ketone -one, Carboxylic acid -oic acid, Ester -oate, Amine -amine