CHEM 213 Lecture Notes - Lecture 14: Hydrogen Bond, Geminal, Chemical Shift
16 Oct 2016
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Document Summary
Depends on how hydrogens are aligned with each other. Transmission is poor if there is no orbital overlap on the two centres. The size of the coupling constant depends on the nuclei and their distance relationship and the karplus relationship Constant magnitude-->certain amount of hertz--> energy is xed-->not dependent on eld. Chemical shift does depend on eld-->absolute frequency in hertz. Easily identify which is which from the coupling constants. Coupling in saturated system = 0 if four bonds away. Exchangeable protons move on and o very quickly about 10^5 per second. Nmr relaxation time is relatively slow, ms-many ms even to seconds. Nmr time scale is 10^-2-10^-3 fastest an nmr can measure. Therefore you lose coupling because coupling requires you to have a xed relationship. Sharp signal is from really fast or really slow average. The more acidic the more delta positive, therefore, higher in chemical shift. Saturated alcohols between 1-5 ppm because not very acidic.
