Chemistry 1301A/B Chapter Notes - Chapter 4: Infrared Spectroscopy, Wavenumber, Spectroscopy

• School: Western University
• Department: Chemistry
• Course: Chemistry 1301A/B
• Professor: Felix Lee

Document Summary

Chapter 4: structure and shape of organic molecules. Energy absorption: because energy levels are quantized, only certain energies are absorbed. Wave number = inverse of wavelength (wave number and energy are directly proportional) Ir spectroscopy: when ir light is absorbed, bonds are vibrationally excited. Ir e(cid:374)e(cid:396)gy is a(cid:271)so(cid:396)(cid:271)ed whe(cid:374) the f(cid:396)e(cid:395)ue(cid:374)(cid:272)y of the light (cid:373)at(cid:272)hes the (cid:862)(cid:374)o(cid:396)(cid:373)al(cid:863) f(cid:396)e(cid:395)uency of the vibration. A(cid:374) ir spe(cid:272)t(cid:396)o(cid:373)ete(cid:396) outputs a(cid:374) ir a(cid:271)so(cid:396)ptio(cid:374) spe(cid:272)t(cid:396)u(cid:373) (cid:271)ut t(cid:396)aditio(cid:374)ally plotted as t(cid:396)a(cid:374)s(cid:373)issio(cid:374) Functional groups: functional groups absorb at different energies because we assume a bong equals 2 atoms between springs. Bond strength (affects k): t(cid:396)o(cid:374)ge(cid:396) (cid:271)o(cid:374)d = highe(cid:396) k = highe(cid:396) f(cid:396)e(cid:395)ue(cid:374)(cid:272)y lighte(cid:396) ato(cid:373)s (c-h) = higher frequency. Mo(cid:396)e s (cid:272)ha(cid:396)a(cid:272)te(cid:396) = st(cid:396)o(cid:374)ge(cid:396) (cid:271)o(cid:374)d hy(cid:271)(cid:396)idizatio(cid:374) is st(cid:396)o(cid:374)ge(cid:396) i(cid:374) the o(cid:396)de(cid:396) sp3< sp2< sp. Mass difference (affects u): bonds between atoms of higher masses vibrate at lower frequencies than bonds between lighter atoms. Heavier atoms connected to spring = lower frequencies. (bigger things move slower)