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活泼氢本身化学位移值就是有一个较大的变动范围吧。
" Z& l0 V, s1 k* L& F! E至于积分值，一般要比按化合物的分子式算出来的比例要小。
) x8 w( E: U7 L y3 N4 F& q: Y原因很多，H交换是一个，积分基线也是一个。前段时间看Simpson的Organic Structure Determination
Using 2-D NMR Spectroscopy，里面有提到：
a7 |3 g% y( Z: r% x/ b
2 Z* t% E3 H8 l) Q- B; r0 f2 vThere are several possible reasons to account for why we observe the
low integral values for 1H’s bound to heteroatoms despite having a
sufficiently long relaxation delay between scans. First, relaxation (T 2 )
may occur to a greater extent for those 1H’s whose signals are broad as
a result of the time delay between the read pulse and the start of the
digitization of the FID. Because a broad resonance in the frequency
domain corresponds to a rapidly decaying signal amplitude in the
time domain, broad resonances will often generate low integrals. A
second possible reason for a low integral value is that baseline correction
of the spectrum may wipe out the edges of broad resonances,
thus subtracting intensity from the peak. A third possible reason for
a low integral value of a 1H on a heteroatom may result from partial
chemical exchange of these 1H’s with deuterons ( 2H’s) in the solvent,
especially if the solvent is deuterated water or methanol 9 I7 j% A( U: n7 I" j% V
[此贴子已经被作者于2009-10-28 19:00:43编辑过] % D& E* X7 d5 Y4 k8 X* ]
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发表于 2008-11-20 15:17:21
发表于 2008-11-20 15:46:39
