Mechanisms in organic chemistry

Question 1

what are stereoelectronic effects?

Answer 1

electronic interactions between orbitals (usually a filled orbital interacting with an empty orbital) that stabilises a particular conformation or transition state

Question 2

what does reactivity and preferred conformation depend upon?

Answer 2

relative stereochemistry of particular electron pairs that can be either bonding or non bonding.

Question 3

What is a SN2 reaction?

Answer 3

Nucleophilic substitutions that happen in one step (when one bond is broken another is formed). The product is inverted

Question 4

What is a SN1 reaction?

Answer 4

Nucleophilic substitution that involves a carbocation intermediate. The nucleophile attacks the carbocation forming the product

Question 5

Stereoelectronic effects definition

Answer 5

Interactions of electronic orbitals in 3D - they are always stabilizing and reflect delocalisation at favourable conformations

Question 6

where does a nucleophile add its electron density to a carbonyl group?

Answer 6

nucleophiles add electron density to the pi* orbital (SN2 adds to the sigma *) forming a new sigma bond

Question 7

what is the anomeric effect?

Answer 7

Any tetrahydropyran bearing an electronegative substituent in the 2-position will prefer that substituent to be axial. It is a stabilizing stereoelectronic effect

Question 8

What is the stereoelectronic preference for conformations

Answer 8

The best lone pair orbital is antiperiplanar to the best acceptor bond

Question 9

What are the relative orders of energy levels for HOMO and LUMO

Answer 9

HOMO is the donor orbitals (availability of electron density is important). LUMO is the acceptor orbital - antibonding orbitals (ability to accept density is important)