14C_s11_lec01_e02_key

A number of signals equal both have three signals in

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Unformatted text preview: Most deshielded carbon 8. (a) Number of signals equal. Both have three signals in their 1H-NMR spectra. (b) Metacide 38. None of the carbons in metacide 38 are equivalent to other carbons in the molecule, resulting in six signals in its 13C-NMR spectrum. EDTA has some equivalent carbons, resulting in just three signals in its 13 C-NMR spectrum. 9. X-ray diffraction can determine the position of atoms in space and therefore any aspect of molecular structure than can be described by atomic positions. The technique cannot count electrons, determine formal charges, or measure energy. (a) That all carbon-chlorine bonds lengths are not equal can be determined (b) That the rings are aromatic cannot be determined. X-ray diffraction cannot ascertain if Hückel's rule is obeyed. (c) The number of atoms lying in the same plane can be determined. (d) The magnitude (in kcal mol-1) of the C–O barrier to rotation cannot be determined. 10. (a) m/z: Mass-to-charge ratio. (b) M: Molecular ion. 11. Silicon. This element causes shielding because of its low electronegativity (EN = 1.8). 12. (a) Splitting is caused by spin-spin coupling between neighboring nuclei within a molecule. (b) For a proton, its proton neighbor can have I = +1/2 or I = -1/2. (c) When a proton Ha has only one neighbor Hb, Ha has two spin flip energies. Hb's spin axis can be parallel or antiparallel to Ha's spin axis. 13. (a) Mass spectrometry does depend on a magnetic field to sort (or focus) ions according to their m/z. (b) Infrared spectroscopy does not depend on a magnetic field. (c) NMR does depend on a magnetic field to influence (or amplify) the spin flip energy. (d) X-ray crystallography does not depend on a magnetic field. 14. Mass spectrum: m/z = 236 (M): Zero or even number of nitrogens. m/z = 237 (M+1): 15.7%/1.1% = 14.3 C14 or C15. m/z = 238 (M+2): < 4% so no sulfur, chlorine, or bromine. Formula (C14): 236 - 168 (C14) = 68 amu for oxygen, nitrogen, and hydrogen. The 1749 cm-1 peak in the IR spectrum is due to a C=O stretch, so the formula must...
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This note was uploaded on 09/06/2011 for the course CHEM 140A taught by Professor Whiteshell during the Fall '04 term at UCSD.

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