Orgo 2 Exam 4

Effect of Neighboring Hydrogens in HNMR

N+1, but the more neighboring hydrogens, the more deshielded the Ha is, meaning that it is shifted slightly downfield.

Coupling constant definition

The distance between Peaks in HNMR (Measured in Hz)

J Value for “Vicinal” Hydrogens

J Values of “cis,” “trans,” and “Geminal” protons

J values for O, p, and m in Benzene rings

Para protons don’t really couple

J for 3 carbon vinylic systems

How to do Splitting tree for multiple Js

Shielding/Deshielding in Benzene ring for EDG

Ortho and para are more shielded (upfield) because resonance effect gives them lone pair while meta is deshielded

Splitting pattern USUALLY for ortho hydrogen

Doublet of doublet

Splitting pattern USUALLY for Meta hydrogen

triplet

Splitting pattern USUALLY for Para hydrogen

Triplet of triplet

J for alkenes and Benzenes

Enol formation from tautomerization

Acidic vs basic ketone tautomerization mechanism

Tautomerization equilibrium position

Bases used for Enolate Formation

NaOEt and t-BuOK are used for reversible enolate formation (t-BuOK is stronger) while NaH and LDA are used for irreversible but greater yield enolate formation

Choice of base when enolate is resonance stabilized

Alpha Halogenation of Enols and Enolates Reagents and Mechanism

Regioselectivity in alpha halogenation

Alpha bromination of carboxyllic acids, esters, or amides

Doesn’t happen with the same reagents as ketones and aldehydes because the enols are unstable

Hell-Volhard-Zelinsky Reaction (Alpha halogenation of COOH) Reagents and mechanism

Reagents are Br2 and PBr3 and second step is H2O (or nucleophile with H)