第3楼2005/03/16
I assume you are talking about the carbon spectrum. When the number of methyl groups increases, the electron claud around the carbon of interest becomes denser, which forms chemical shielding, thus it needs higher magnetic power for its resonance (that is, its chemical shift becomes higher).
第4楼2005/03/17
照你的说法,化学位移应该越低才对呀?因为高磁场对应的是低位移哦
第5楼2005/03/18
In this equaiton: B=B0(1-delta), delta is the shielding factor, if delta increases (meaning the shielding gets higher), the magnetic field strength the nucleus "feels" is lower, that is the chemical shift is higher.In a normal Fourier Transformation NMR spectrum, the chemical shift increases from the right hand side to the left.
第6楼2005/03/18
这位老师,你的公式是对的,理解也是对的,但是结论错了。
任何原子都有固有的进动频率,或者说在固有的场强(假设为Bx)下才会发生进动。但是由于原子周围的磁屏蔽作用,使得原子自身感受的场强(B)与外界施加的场强(B0)不一致(略微低于B0),因此需要提高外界施加的场强(B0),以使得B=Bx,从而使原子产生进动。因此,对于有屏蔽作用的原子,其发生进动时,外界场强B0相对的要更高些,化学位移则更低些。
第8楼2005/03/21
daiyi说的对,分析是正确的,但是结论错了,正是由于the magnetic field strength the nucleus "feels" is lower,所以化学位移应该低一些才对。