Organic Chemistry Flashcard Quiz

Question 1

What is the Markovnikov rule?

Accepted Answer

In electrophilic addition to an alkene, the electrophile (e.g., H⁺) adds to the less-substituted carbon (the one with more hydrogens), while the nucleophile adds to the more-substituted carbon. This produces the more stable carbocation intermediate.

Question 2

What is the key difference between SN1 and SN2 reactions?

Accepted Answer

SN1 is a two-step mechanism that proceeds through a planar carbocation intermediate. It is favored by tertiary substrates and polar protic solvents, and gives racemic products. SN2 is a concerted one-step mechanism with simultaneous bond breaking and back-side attack. It is favored by primary substrates and polar aprotic solvents, and gives inversion of configuration.

Question 3

What are the products of ozonolysis with reductive workup?

Accepted Answer

Ozonolysis with reductive workup (Zn/H₂O or Me₂S) cleaves the C=C double bond. A terminal alkene (RCH=CH₂) gives an aldehyde and formaldehyde. An internal alkene (R₁CH=CHR₂) gives two aldehydes. A disubstituted alkene (R₁R₂C=CR₃R₄) gives two ketones.

Question 4

What NMR chemical shift range do aldehyde protons appear in?

Accepted Answer

Aldehyde protons (CHO) appear in the ¹H NMR spectrum at δ 9–10 ppm. They are highly deshielded due to the electron-withdrawing carbonyl group and the anisotropic effect of the C=O bond.

Question 5

How does the Wittig reaction form alkenes?

Accepted Answer

The Wittig reaction uses a phosphonium ylide (R₂C=PPh₃) to react with an aldehyde or ketone. The ylide acts as a nucleophile, attacking the carbonyl carbon to form a four-membered oxaphosphetane intermediate, which collapses to give an alkene and triphenylphosphine oxide. Stabilized ylides give (E)-alkenes; non-stabilized ylides give (Z)-alkenes.

Question 6

What is the Zaitsev rule in elimination reactions?

Accepted Answer

Zaitsev's rule states that in elimination reactions (E1 and E2), the major product is the more substituted (more stable) alkene. This is because the transition state leading to the more substituted alkene has partial double-bond character stabilized by hyperconjugation and inductive effects.

Organic Chemistry Exam Prep