PS1AnswerKey

PS1AnswerKey - Problem Set 1 Answer Key Problem 1(a = BH 2...

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Unformatted text preview: Problem Set 1 Answer Key Problem 1 (a) = BH 2- I h (1 point) C 5 axis through each pair of opposite B atoms C 3 through centers of opposite triangles C 2 through middle of opposite B-B bonds Planes of symmetry containing C 5 axis and containing one of B-B bonds. S 10 axis same as C 5 . Center of inversion in center of molecule S 6 axis coaxial with C 3 ’s (Total: 7 points) (b) = BH = CH ortho meta para C 2v D 5d C 2v (1 point each) (c) C 3v D 3d C s 3 signals 6 signals 1 signals (1 point each) C s : plane containing middle C atom, equidistant from other two (contains 3B’s, 1 point) C 3v : C 3 through center of triangle of C atoms; planes of symmetry containing one C and bisecting opposite C-C bond. (2 point) D 3d : Same as C 3v but also C 2 axis through opposite B-B bonds, i in center. (2 point) C 2h D 2h C 2v C 5v 2 signals 3 signals 2 signals 3 signals = BH = CH = NH (1 points each; only one possibility for each point group shown, many possible) None of the molecules in (c) are chiral (1 points) C 5v : C 5 axis through C and opposite B atom. Planes containing C 5 axis and one of the C- B bonds (there are five). (2 point) D 2h : C 2 through middle of opposite C-C bonds. Perpendicular C 2 ’s through middle of opposite B-B bonds. Horizontal plane of symmetry containing four B atoms (and not bisecting C-C bonds). (2 point) (d) Number of NMR signals shown above. (1 point per molecule, 7 points total) Problem 2 a) 1,3,5,7-tetrafluorooctatetraene F F F F c) [Ru(bipy) 3 ] 2+ N N Ru N N N N d) C 7 H 11 Cl 5 Cl Cl Cl Cl Cl e) trans-1,4-dibromocyclohexane Br Br Answers: a) S 4 , achiral. The S 4 axis down the center of the molecule precludes chirality. (2 points) b) D 3 , chiral. (3 points) c) C 1 , chiral. (3 points) d) C 2h , achiral. The σ h plane through both Br atoms and the C atoms attached to them precludes chirality. (3 points (1 point each for chirality) Problem 3 1 2 3 4 5 6 7 8 9 10 Answers: a) 4 C 3 axes, 6 σ d planes, and 3 S 4 axes, 3 C 2 axes (5 points). b) One C 3 axis goes through the center of the molecule and C 1 , and it leaves 1 H atom unmoved. One σ d plane contains C 1 , C 3 , C 6 , and C 9 , and it leaves 4 H atoms unmoved....
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PS1AnswerKey - Problem Set 1 Answer Key Problem 1(a = BH 2...

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