SPECTROSCOPIC IDENTIFICATION OF ORGANIC COMPOUNDS

If the wavelength (the distance between the wave maxima or alternate nodes) is measured in centimeters, v is expressed in centimeters per second (cm/s). For radiation traveling in a vacuum, v becomes a constant, c (c 3 X 10 ° cm/s), for all wavelengths. When electromagnetic radiation traverses other media, however, the velocity changes. The ratio of the speed in a vacuum, c, to the matrix velocity, v, is termed the refractive index, n, of the material  

Since n is frequency dependent, the frequency af which the refractive index is measured must be specified. Frequency, however, has been shown to be independent of the medium and, therefore, remains constant. Wavelength thus varies inversely with n. 

Since the velocity of elecfromagnefic radiation in a vacuum is normally greater than that in any other medium, n will generally be greater than 1 at all frequencies. Thus, the wavelength must become shorter for a particular frequency when measured in any matrix. 

Frequency can be considered to be a more fundamental property of radiation because it is independent of the medium. This property also requires that the energy E associated with the radiation be matrix independent because E is directly proportional to frequency by 

The vibrational states present in molecules can be excited by absorption of photons. The nuclear masses and bond force consfants determine the separation of these states and, therefore, fhe energies of fhe phofons involved in the absorption process. The corresponding radiation frequencies fall predominantly in the IR region Hz) of fhe electromagnetic spectrum. 

---

Butane, 2-Butene, 2-Butyne R. M. Silverstein, G. C. Bassler and T. C. Morril, Spectroscopic Identification of Organic Compounds, 5th ed. (Wiley, New York, 1991), 236-239. 

Silverstein RM, Bassler GC, Morrill TC. 1981. Spectroscopic identification of organic compounds. 4th edn. John Wiley Sons, New York, pp 308. 

Silverstein, R.H., Bassler, G.C., and Morrill, T.C., Spectroscopic Identification of Organic Compounds, 6th ed., John Wiley Sons, New York, 1998. 

K. Feinstein, Guide to spectroscopic identification of organic compounds, CRC Press, Boca Raton, 1995, ISBN 0849394481. 

Silverstein, R.M. and Webster, F.X. (1997) Spectroscopic Identification of Organic Compounds, 6th Edn, John Wiley and Sons Inc., Chichester. 

---