preface to fifteenth edition

7.18 SECTION 7
TABLE 7.8
Mass Absorption Coefficients for K 1 Lines and W L 1 Line (Continued)
Emitter
wavelength, Å
Ag K 1
0.559
Mo K 1
0.709
Cu K 1
1.541
Ni K 1
1.658
Co K 1
1.789
Fe K 1
1.936
Cr K 1
2.290
W L 1
1.476
Absorber
79 Au 67 113 209 252 307 377 584 186
80 Hg 69 117 218 263 321 394 609 194
81 Tl 72 121 227 275 334 411 635 203
82 Pb 74 125 236 286 348 428 662 211
83 Bi 78 129 247 298 363 446 690 220
84 Po 131 258 311 380 466 721 230
85 At 269 325 397 487 753 240
86 Rn 85 281 340 414 509 787 251
87 Fr 89 294 356 433 532 823 262
88 Ra 91 307 372453 556 861 274
89 Ac 322 389 474 582 900 287
90 Th 97 337 408 497 610 944 301
91 Pa 353 427 520 639 988 315
92U 104 372 450 548 673 898 332
93 Np 392474 578 709 945 350
94 Pu 54 418 505 615 755 835 373
7.2 ULTRAVIOLET-VISIBLE SPECTROSCOPY
Molecules with two or more isolated chromophores (absorbing groups) absorb light of nearly the
same wavelength as does a molecule containing only a single chromophore of a particular type. The
intensity of the absorption is proportional to the number of that type of chromophore present in the
molecule. Representative chromophores are given in Table 7.9.
The solvent chosen must dissolve the sample, yet be relatively transparent in the spectral region
of interest. In order to avoid poor resolution and difficulties in spectrum interpretation, a solvent
should not be employed for measurements that are near the wavelength of or are shorter than the
wavelength of its ultraviolet cutoff, that is, the wavelength at which absorbance for the solvent alone
approaches one absorbance unit. Ultraviolet cutoffs for solvents commonly used are given in Table
7.10.
Appreciable interaction between chromophores does not occur unless they are linked directly to
each other, or forced into close proximity as a result of molecular stereochemical configuration.
Interposition of a single methylene group, or meta orientation about an aromatic ring, is sufficient
to insulate chromophores almost completely from each other. Certain combinations of functional
groups afford chromophoric systems which give rise to characteristic absorption bands.
Sets of empirical rules, often referred to as Woodward’s rules or the Woodward-Fieser rules,
enable the absorption maxima of dienes (Table 7.11) and enones and dienones (Table 7.12) to be
predicted. To the respective base values (absorption wavelength of parent compound) are added the
increments for the structural features or substituent groups present. When necessary, a solvent correction
is also applied (Table 7.13).