2: Identification of Ligand Exchange Mechanisms and Applications in Synthesis

Question 1

A wide range of limiting rates for different incoming Y ligands implies what

Answer 1

Reaction mechanism as Ia

Question 2

For a D mechanism, what is the expected sign of the activation parameters ΔS‡ and ΔV‡

Answer 2

Both ΔS‡ and ΔV‡ will be positive

Question 3

In a D mechanism, more species are present where

Answer 3

in the transition state and these will occupy a larger volume than the starting reagents.

Question 4

The rate of ligand exchange for Group 1 elements decreases when

Answer 4

As the group is descended.

Question 5

Ligand substitution in square planar transition metal complexes always proceeds via what mechanism

Answer 5

A dissociative mechanism

Question 6

What does exchange in a square planar complexe involve

Answer 6

associative steps

Question 7

As you descend group 1, what happens to the rate of exchange

Answer 7

it increases due to decreasing charge density of the cation

Question 8

what does a wide range of limiting rates for different leaving Y ligands suggest

Answer 8

That bond-breaking dominates. But we would need the rate for solvent exchange [i.e. Y = H2O] to be able to distinguish between Id and D.

Question 9

why is ΔV‡ easier to detect than ΔS‡

Answer 9

ΔV‡ is measure directly from the gradient of a graph, while ΔS‡ can only be obtained by extrapolation to where the graph crosses the y-axis which subject to larger errors.

Question 10

An electron transfer between two transition metal centres that involves bond-forming and bond-breaking is known as

Answer 10

Inner sphere electron transfer

Question 11

which halide exhibits largest trans effect

Answer 11

An iodide ion is the largest and so most polarisable, and hence exhibits the largest trans-influence of the halides