Organic Chemistry 2 Exam 2

Conjugated system

Any double-single-double bond

Allene

Double-double bond

NBS

• Good source of bromine

• hv required

• CCl₄ solvent

• Allylic bromination

Allylic position

-C=C-C (the C on the right is the Allylic C)

Conjugated dienes

• More stable

• Shorter bond length

Types of reactions of conjugated dienes

1. Electrophilic Addition

2. Diels Alder Reaction

(Has Markovnikovs addition)

Electrophilic addition of conjugated Dienes has which products

• Kinetic

• Thermodynamic

Kinetics product

• 1,2- adduct

• Has more % at Room temperature

Thermodynamics product

• 1,4- adduct

• Has more % at high temperature

Formal charge formula

(# of valence electrons) - (lines + dots)

Diels-Alder Reaction

• Diene

• Dienophile

Diene

• Has 2 carbons with 2 double bonds

• One Double bond is used to form bond with dienophile while other moves to single bond to form double bond ( 1 will go away)

Dienophile

• Has 2 carbons with a double bond and an Electron withdrawing group

Conditions of Diene

• s-trans → s-cis

• locked in s-cis

• locked in s-trans

• hard to reach/react

Diene that goes from s-trans to s-cis

Reactive but slow reaction

Diene that is locked in s-cis

• Best position for dienes

• Very reactive

Dienes locked in s-trans

Unreactive

Dienes that are unable to reach Dienophiles

• Cannot adopt s-cis conformation because of steric hindrance

• Unreactive

If there is no electron withdrawing group then the molecule is not a…?

Dienophile

T or F- having more electron withdrawing groups on the Dienophile is better

True

T or F- The stereochemistry of Dienophile changes after reacting with dienes

False

Axial position

• Straight

• Endo

Equatorial position

• Slanted

• Exo

T or F- endo position is more favorable than exo position

True

Toluene

CH₃

Phenol

OH

Aniline

NH₂

Benzoic acid

CO₂H

Benzaldehyde

CHO

Benzonitrile

CN

Benzyl

-CH₂–

Benzene

Acetophenone

COCH₃

Nitrobenzene

NO₂

Phenyl

Name for when benzene is connected to something else

Ortho

1,2

Meta

1,3

Para

1,4

Benzene is…?

Unusually very stable

Huckel’s rule

Benzene is a conjugated aromatic compound, aromatic compounds are:

• Planar

• Cyclic

• Conjugated

• Has a total of 4n+2(pi) electrons (where n= whole numbers)

4 pi electrons means the compound is..?

Anti aromatic

Anti aromatic

• Less stable than aromatic

• Very reactive

Cyclooctatetraene

Anti-aromatic because it is not planar and is flat

What contributed to the pi electron system besides pi bonds(double bonds)

Electrons and lone pairs

+, ^.., and ^.

Leave empty sp² orbital To make molecule aromatic

Heterocycles

When carbon is replaced by a nitrogen, sulfur, etc. which makes the molecular not similar

When a nitrogen has lone pairs but is near a double bonds, it…?

Is not in the pi system

T or F- A (+) sign adds a pi electron

False

If lone pair is in sp² orbital, it is..?

Not a part of the pi system

Aromatic vs anti-aromatic

Aromatic is stable and not a solvent because it is not reactive whereas anti-aromatic is the opposite

Lewis acid

Electron accepter

Types of reactions for alkenes vs aromatics

• Alkenes: Electrophilic addition

• Aromatics: Electrophilic aromatic substitution (EAS)

Bromination

• —Br₂/FeBr₃ →

• Product is Br attached to benzene

Chlorination

• —Cl₂/FeCl₃–>

• Product is Cl attached to benzene

Iodination

• —I₂/CuCl^₂—>

• Product is I attached to benzene

Electrophile

• Lewis acid

• Accept electrons

• Has a Positive charge

Base

• Has the negative sign

• The catalyst after gaining an atom

Nitration electrophile

NO₂ with 2 double bonds attached to each O and a positive charge on N

Nitration

• —HNO₃/H₂SO₄–>

• Product is NO₂ attached to benzene

Sulfonation

• —SO₃/H₂SO₄–>

• Product is SO₃H

• Electrophilic is HSO₃⁺ (sulfanyl)

Friedle-Crafts Alkylation

• —alkyl halide/AlCl₃–>

• Product is alkyl halide attached to benzene

Friedel-Crafts Acylation

• —Acyl Halide/AlCl₃–>

• Product is acyl halide attached to benzene

Nitric acid

• Used as the first step/reaction in nitration

• HNO₃

Prep step

• Always required

• Before the first step in an EAS reaction

• X₂ breaks bond and attached to Lewis acid catalyst and forms a strong Electrophilic and base

Resonance creates a stable…?

Carbocation

Catalyst

• Speeds up a reaction

• Shown in first step and comes back as a product because it is not used up

The energy of addition reactions are ___ than the energy of substitution reactions

Greater

Friedel Crafts Limitations

1. Only works with alkyl Halides (not Aryl halides, double bonds, or cyclo structure)

2. Difficult to stop reaction after a single substitution (no alkylation)

3. Electron rearrangement may occur (primary → secondary)

Acyl

RCO

Ortho and para-directing

Activating

Meta-directing

• Deactivating

Halogens

• Weakest out of the ortho para directing

• F,Cl,Br,I

Sigma Donors

• Second strongest out of the ortho para directing

• -R

• Alkyl (ex. CH₃)

• Aromatic ring/benzene

• Aryl (RCO)

Pi donors

• Strongest out of ortho para directing

• NH₂

• OH

• OR

• NHCOCH₃

• Non-binding electron pairs

Carbonyls

• Weakest out of the meta-directing

• COR

• COOH

• COOR

Other in the meta directing

• Strongest in meta directing

• SO₃H

• C (triple bond) N

• NO₂

• N⁺R₃

Steric hindrance when doing additivity of effects

Nucleophilic Aromatic Substitution

• Occurs in 2 steps

• Not SN₂

• Forms carbanion (intermediate)

• Halogen(Good leaving group)

• EWG in ortho or para position to the leaving group

Oxidation of aromatic compounds

• KMNO₄ (strong oxidizing agent)

• Benzylic hydrogen

Benzylic hydrogen

• Hydrogen that is attached to the first carbon

• If there are 2 Benzylic hydrogens, reaction happens twice

Bromination of alkylbenzene side chains

• Considered to be oxidation

• Adding a halogen

• NBS (N-Bromosuccinamide)

• Radical reaction

Reduction of aromatic compounds

• Changes all oxygen to Hydrogen when friedel crafts acylation is involved (RCO)

• —H₂, Pd/C or Pt or Rh/C/ ethanol—>