Clayden pp. 851 – 904

Now 60% of the way through Clayden et. al.  It just keeps getting better and better.  All the notes below are given in attempt to make the second edition (which is in the works) even better. Some are about things I don’t understand.  I hope they don’t come across as querulous or picky.

If you’re thinking of postponing purchase of the current edition (which is now 9 years old), you should know that I have it on very good authority that the second edition won’t be out until the spring of 2012 !!!   

Please look at comment #2 of what’s listed about pp. 881 – 904 below and help out if you can. 

p. 851 — It’s great to see an explicit page reference to a discussion occurring (nearly 400 pages) earlier.  Malheureusement the reference is off by 1 (it should be p. 471).

p. 853 — “rapid ring flipping equilibrates all these conformers” Well, how rapid is this.
p. 857 — “the incoming phenyl group also prefers the equatorial approach”  I think that ‘equatorial approach’ is a poor term and, worse, misleading — although the phenyl group winds up equatorial, the first constitutent of the ring it bumps up against are the axial hydrogens next to the carbonyl.   Approach the other way is blocked by the equatorial methyl group.

p. 857 — (bottom paragraph) ‘formation of a tertiary benzylic cation’ — it’s a thiophenylic cation (if such a term exists).

p. 859 — “a chair is better than a twist boat”  — any idea how much better in kiloJoules/mole.  Surely the computational organic chemists have been at work.

p. 861 — “Any reaction that is reversible and that forms a six membered ring can be expected to put as many substituents as possible in the thermodynamically favorable equatorial position.”  This would be a good time to note that glucose (Nature’s choice) has exactly this property — all the substituents can be equatorial (and are).  There is only one other hexose for which this is true. 

p.871 — “After the first alkylation, the enamine prefers to reform on the less substituted side”.  Why, I though more highly substituted double bonds were of lower energy. 

p. 872 — In the iodolactonization reaction, why does the nucleophile attack the more substituted end of the halonium ion forming a 5 membered ring, rather than the other end forming a 6 membered ring?

p. 874 — The synthesis of the C/D rings os the steroid nucleus starting here, is just marvellous.  Who did it?

p. 878 — What happens to the acac’s in the vanadium complex?  Don’t they get in the way? 

p. 880 — Problem #8 — The selenium chemistry needed to solve the problem isn’t introduced until p. 1271.  

pp. 881 – 902 Ch. 34  Three general points.

    l. The blizzard of terms (enantiotopic, diastereotopic,  steroselective, prochirality, stereospecific, enantiomer, diastereoisomers, homotopic) isn’t particularly helpful (to me at least).   It’s better just to look at the stereochemistry (conformations etc.) of any given molecule and figure out what happens.  This is something I was always good at, and I can still see the damn things moving about in space.  It irritated the hell out of people. 

    2. The stereochemistry of the metal ions is missing.  We have innumerable discussions regarding the disposition of orbitals in space and how they determine reactivity, yet when we get to chelating metal ions in space (p 883 –> ) there is not a word about what the orbitals used to chelate the organic compounds look like or how they are disposed in space.  As far as I can tell Hegedus’s and Hartwig’s books on organometallic chemistry don’t have much either.  Do any of you out there have a good reference on metal ion stereochemistry as it relates to organic chemistry? 

     3. The pointers back to specific pages throughout the chapter are quite helpful. 

p. 881 — You’ve got a great example of stereospecificity and stereoselectivity with a reaction in the same molecule (epoxidation of a double bond on p. 895) you might point to it (or have it here and say you’ll discuss it later).

p. 889 — third line from the bottom — ‘proecjction’ 

p. 892 — Something is seriously wrong. “Sulfur is the electronegative atom”, yet looking in the back you have the electronegativity of S at 2.58, C at 2.55.  There must be another (and better) explanation.

p. 893 — “Changing the metal from sodium to zinc” — the previous metal given was Lithium not sodium.

p. 893 — the third line of structures appears to be a serious case of bait and switch, with two more phenyl groups appearing in reactants and products than the example which had one phenyl and a thiomethyl group. 

p. 897 — In the second line of structures, the trans methyl group disappeared in the transition state and in the final product. 

p.900 — It isn’t at all obvious (to me anyway) why you’d expect the transition state to be chairlike.  Where are the nonbonding oxygen electrons in an enolate — they’d have to be tetrahedral the way they’re drawn here. 

p. 904 — Problem #6 — The stereochemistry of the methyl group isn’t given in the initial description of the problem.  It disappears in the transition state to the iodolactone.  Very unsatisfying problem.  
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