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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。 ' K+ e4 B W) w
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。 " X3 S7 A/ O! u
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： * `4 w( ]* H9 P! X v
' t6 g/ b; N1 s0 { @! j) iThere 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
7 z0 Q: ~& N5 T# y[此贴子已经被作者于2009-10-28 19:00:43编辑过]
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发表于 2008-11-20 15:17:21
发表于 2008-11-20 15:46:39
