CHEM 2301 Lecture 41: 14.4-14.7 (4/30)
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"14.4 nuclear shielding + H NMR chemical shifts!
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"chemical electronic environment !
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"‘H"C"F"P!
""H"N!
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"‘H NMR!
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"internal standard" " TMS tetramethylsilane !
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"4 features of ‘H NMR spectrum !
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"1. Position of signals !
"2. Number of signals !
"3. Intensity of signals !
"4. Spin-spin splitting !
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"14.5 effect of molecular structure
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"shielding/deshielding!
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"""""""-e- induced magnetic field opposing Bo!
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"""""""-decreases field strength !
"""""""-lower frequency required for spin flip !
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"""""""-shielding shifts a proton signal upfield (close to 0)"!
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"CH3Cl!
"""""""- H feels less e- density !
"""""""- deshielded (compared to CH4)!
"""""""- shifts signals downfield (higher frequency for resonance)!
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"Fig. 14.8
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"aromatic ring!
"""" Vinyl proton !
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Document Summary
14. 4 nuclear shielding + h nmr chemical shifts chemical electronic environment. 4 features of h nmr spectrum: position of signals, number of signals, intensity of signals, spin-spin splitting. Shielding shifts a proton signal up eld (close to 0) Shifts signals down eld (higher frequency for resonance) Vinyl proton benzene (alkene -> similar) (cid:12254) (cid:12254) (cid:12254) Proton deshielded +shift down eld move in circular path (fig. 14. 9 -> ring current) alkynes (cid:12254) (cid:12254) (cid:12254) pi e- creates magnetic eld that opposes bo. 14. 6 interpreting h nmr spectra number of signals -> number of di erent types of protons. Ch3ch2ch2ch2ch3 replace c-h > c-z (test group) same compound or enantioners -> z protons are equivalent homotopic enantiotopic diasteriomers or constitutional isomer -> non-equivalent diastereotopic heterotopic. Ch3ch2ch2ch2ch3 alkenes + cycloalkanes draw in all hs -> equivalent only if cis/trans to same group. 14. 7 spin-spin splitting single absorption peak -> singlet doublet.
