CHEM 2301, Final Exam, Simple Alkyne Mechanisms, Aromatic Compounds, Conjugation of Allylics and Dienes

Simple Alkyne Mechanisms

Simple Alkyne Mechanism for Hydrohalogenation

-C≡C- → -CH2-CHX2

Simple Alkyne Mechanism for Halogenation

C≡C → X₂C-CX₂

Simple Alkyne Mechanism for Hydrogenation

C≡C → H₂C-CH₂

Simple Alkyne Mechanism for Ozonolysis

C≡C → HO-C=O + HO-C=O

Simple Alkyne Mechanism for Hydration

C≡C → H₂C-C=O

Simple Product Alkyne Mechanism for E2

XHC-CHX → C≡C

Simple Product Alkyne Mechanism for Alkylation

C-C≡C- → C-C≡C-C

The reagent of alkyne Hydrohalogenation

HX (slower than alkene)

The reagent of alkyne Halogenation

X₂

The reagent of alkyne Hydrogenation

H₂ w/ a catalyst (Pt, Pd, CaCO₃

The reagent of alkyne Ozonolysis

1) O_3, 2) H₂O

The reagent of alkyne Hydration

H₂O w/ Hg²⁺ or H₂SO₄

The reagent of alkyne E2

1) NaNH₂, 2) H₂O

Rxn MUST run to completion

The reagent of alkyne Alkylation

1) NaNH₂, 2) H₃C-X

MUST be 1° or methyl

The selectivity of alkyne Hydrohalogenation

Markovnikov

The selectivity of alkyne Halogenation

Anti

The selectivity of alkyne Hydrogenation

Syn

The selectivity of alkyne Hydration

Markovnikov

____ and ____ are possible mechanisms with benzene rings.

hydrogenation, @ high temperature, and ozonolysis, from O₃’s high energy.

Aromatic Ring Physical Properties

• no polarity

• low m.p. and b.p.

• reflects visible light

Benzaldehyde

Benzoic Acid

Phenol

Aniline

Aromatic compounds must have…

2, 6, 10, 14… electrons.

These are abnormally stable and their intermediates form easily. Avoids rxn’s where aromaticity is disrupted.

Anti-Aromatic compounds

4, 8, 12, 16… electrons

These are abnormally unstable

Allylic intermediates are ____ and ____ stable compared to other intermediates.

faster and more stable

Structure of Dienes

C=C-C=C

the middle C-C bond is shorter than a single bond.

Prefers to form E1/E2

Alternative Dienes

-C=C=C-, with double bonds immediately connected, this is less stable.

C=C-C-C=C, double bonds aren’t close enough. Acts like normal alkenes.

1,2-Diene Addition

kinetic product

H-C-CX-C=C

forms faster @ low temperatures

Monosubstituted

1,4-Diene Addition

thermodynamic product

forms slow @ low temperatures speeds up @ 40°C.

Trisubstituted, more stable

The following counts as 2 electrons

a lone pair, an anion, double bond