Alkanes

4. Steric bulk. How strained are the alkanes (t-Bu)₃C-R, ranging from R = H to R = t-Bu? How about the same series for the 1,2-disubstituted alkenes cis-t-Bu-CH=CH-R?

29. Do a complete MM analysis of compound A when R = H and when R = CH₃. Do the same for R = H and R = CH3 for system B. Compare your answers with the calculated and experimental quantities in the literature citation; be sure to see the article for which conformations are to be calculated - do the relatively stable conformations only.

30. A recent article discusses the conformational analysis of the material shown to the right, incorrectly called in the article by a non-IUPAC name: 1,1,2-tri-t-butylethane. Do a complete conformational analysis of rotational possibilities about the C₁-C₂ bond and compare your results (energies, angles, bond lengths, etc.) with those in the cited article.

33. Do a complete conformational analysis (energies, geometries, etc.) of molecules with quaternary carbons: e.g. ranging from (CH₃CH₂)₄C through Et_xCMe_y to (CH₃)₄C; be sure to see the article for which conformations are to be calculated.

98. The 2,3-dihalobutanes have two stereogenic centers. Do MM calculations of the energies and dihedral angles (between the C-CH₃ bonds) of all three staggered conformations for both the R,S (meso if X = Y, erythro if X ¬= Y) and R,R compounds (dl or threo); do the calculations for the five compounds X = Y = F; X = F, Y = Cl; X = F, Y = Br; X = Y = Cl; X = Y = Br; compare your results with the experimental and calculated results in the cited reference.

163. A recent article contains computations on all of the available staggered conformations for many straight-chain hydrocarbons. This MMX problem consists of doing complete conformational analyses of pentane and hexane. For each, use the symbols G and A to represent gauche and anti arrangements at the various four-carbon units. Thus, for pentane there will be the AA conformation (anti for C₁ - C₄ and anti for C₂ - C₅), the AG, etc.; pay particular attention to the GG and GG' conformations (G represents a dihedral angle near 60^o and G' represents a dihedral angle near -60^o) to see if there are some "abnormally large" dihedral angles. For hexane, one will need three descriptors for each conformation (e.g., AAA, AAG, AGA, etc.) corresponding to C₁-C₄, C₂-C₅, and C₃-C₆. Compare your answers with those in the reference.

201. The rather simple looking molecule to the right, tricyclohexylmethane, presents a difficult conformational analysis problem. Even if one keeps all three rings as chairs, there are seven distinct conformations corresponding to gauche (in either a + or - direction) and anti dihedral relationships of the several H-C-C-H units; one H-C is at C1 of each ring; the other C-H is at the central methine carbon. Compute the energies and structures of these seven structures and compare your answers with those in Table I of the cited reference; comment on similarities and differences observed.

223. In a recent article is the surprising claim that the gauche conformation of 9,9'-bifluorenyl (1) is more stable than the anti. Do calculations on these two conformations and comment on the factors leading to a difference in energy between them. Then, do an analogous study on the indenyl dimer 2 in both its meso and dl stereoisomeric forms; note that the latter will have two different gauche conformations.

235. 1,5-Hexadiene (to the right) has "free rotation" about various single bonds. One can have anti or gauche staggered conformations about the central C3-C4 bond on top of which are various rotamers corresponding to rotation about C₂-C₃ and C₄-C₅ (conformations A - E in the article). Calculate the energies and structures of all five conformations and compare your results with both the molecular mechanics and ab initio results in Tables 4 and 5. Discuss similarities and differences.

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