SPECTROSCOPY					7.19
TABLE 7.9 Electronic Absorption Bands for Representative Chromophores
Chromophore	System		max			max
Acetylide	9C#C9		175–180	6 000
Aldehyde	9CHO		210	strong
			280–300	11–18
Amine	9NH2		195	2 800
Azido	C "N 9		190	5 000
Azo	9N"N 9		285–400		3–25
Bromide	9Br		208			300
Carbonyl	C "O		195	1 000
			270–285	18–30
Carboxyl	9COOH		200–210	50–70
Disulfide	9S9S9		194	5 500
			255			400
Ester	9COOR		205			50
Ether	9O9		185	1 000
Ethylene	9C"C9		190	8 000
Iodide	9I		260			400
Nitrate	9ONO2		270 (shoulder)			12
Nitrile	9C#N		160
Nitrite	9ONO		220–230	1 000–2 000
			300–400			10
Nitro	9NO2		210	strong
Nitroso	9NO		302			100
Oxime	9NOH		190	5 000
Sulfone	9SO2 9		180
Sulfoxide	S "O		210	1 500
Thiocarbonyl	C "S		205	strong
Thioether	9S9		194	4 600
			215	1		600
Thiol	9SH		195	1 400
	9(C"C)2 9 (acyclic)		210–230	21 000
	9(C"C)3 9		260	35 000
	9(C"C)4 9		300	52 000
	9(C"C)5 9		330	118 000
	9(C"C)2 9 (alicyclic)		230–260	3 000–8 000
	C"C9C#C		219	6 500
	C"C9C"N		220	23 000
	C"C9C"O		210–250	10 000–20 000
			300–350		weak
	C"C9NO2		229	9 500
Benzene			184	46 700
			204	6		900
			255			170
Diphenyl			246	20 000
Naphthalene			222	112 000
			275	5		600
			312			175
Anthracene			252	199 000
			375	7		900
Phenanthrene			251	66 000
			292	14		000
Naphthacene			272	180 000
			473	12		500

7.20		SECTION 7
TABLE 7.9 Electronic Absorption Bands for Representative Chromophores (Continued)
Chromophore	System		max		max
Pentacene			310	300 000
			585	12	000
Pyridine			174	80 000
			195	6	000
			257	1	700
Quinoline			227	37 000
			270	3	600
			314	2	750
Isoquinoline			218	80	000
			266	4	000
			317	3	500

TABLE 7.10 Ultraviolet Cutoffs of Spectrograde Solvents

Absorbance of 1.00 in a 10.0 mm cell vs. distilled water.

	Wavelength,		Wavelength,
Solvent	nm	Solvent	nm
Acetic acid	260	Hexadecane	200
Acetone	330	Hexane	210
Acetonitrile	190	Isobutyl alcohol	230
Benzene	280	Methanol	210
1-Butanol	210	2-Methoxyethanol	210
2-Butanol	260	Methylcyclohexane	210
Butyl acetate	254	Methylene chloride	235
Carbon disulfide	380	Methyl ethyl ketone	330
Carbon tetrachloride	265	Methyl isobutyl ketone	335
1-Chlorobutane	220	2-Methyl-1-propanol	230
Chloroform (stabilized	245	N-Methylpyrrolidone	285
with ethanol)		Nitromethane	380
Cyclohexane	210	Pentane	210
1,2-Dichloroethane	226	Pentyl acetate	212
Diethyl ether	218	1-Propanol	210
1,2-Dimethoxyethane	240	2-Propanol	210
N,N-Dimethylacetamide	268	Pyridine	330
N,N-Dimethylformamide	270	Tetrachloroethylene	290
Dimethylsulfoxide	265	(stabilized with thymol)
1,4-Dioxane	215	Tetrahydrofuran	220
Ethanol	210	Toluene	286
2-Ethoxyethanol	210	1,1,2-Trichloro-1,2,2-	231
Ethyl acetate	255	trifluoroethane
Ethylene chloride	228	2,2,4-Trimethylpentane	215
Glycerol	207	o-Xylene	290
Heptane	197	Water	191

SPECTROSCOPY

7.21

TABLE 7.11 Absorption Wavelength of Dienes

Heteroannular and acyclic dienes usually display molar absorptivities in the 8000 to 20 000 range, whereas homoannular dienes are in the 5000 to 8000 range.

Poor correlations are obtained for cross-conjugated polyene systems such as

The correlations presented here are sometimes referred to as Woodward’s rules or the Woodward-Fieser rules.

Base value for heteroannular or open chain diene, nm	214
Base value for homoannular diene, nm	253
Increment (in nm) for
double bond extending conjugation	30
Alkyl substituent or ring residue	5
Exocyclic double bond	5
Polar groupings:
-O-acyl	0
-O-alkyl	6
-S-alkyl	30
-Cl, -Br	5
-N (alkyl)2	60
Solvent correction (see Table 7.13)
Calculated wavelength	total

Ring substitution on the benzene ring affords shifts to longer wavelengths (Table 7.14) and intensification of the spectrum. With electron-withdrawing substituents, practically no change in the maximum position is observed. The spectra of heteroaromatics are related to their isocyclic analogs, but only in the crudest way. As with benzene, the magnitude of substituent shifts can be estimated, but tautomeric possibilities may invalidate the empirical method.

When electronically complementary groups are situated para to each other in disubstituted benzenes, there is a more pronounced shift to a longer wavelength than would be expected from the additive effect due to the extension of the chromophore from the electron-donating group through the ring to the electron-withdrawing group. When the para groups are not complementary, or when the groups are situated ortho or meta to each other, disubstituted benzenes show a more or less additive effect of the two substituents on the wavelength maximum. Calculation of the principal band of selected substituted benzenes is illustrated in Table 7.15.

7.22

SECTION 7

TABLE 7.12 Absorption Wavelength of Enones and Dienones

Base values, nm
Acyclic , -unsaturated ketones	215
Acyclic , -unsaturated aldehyde	210
Six-membered cyclic , -unsaturated ketones	215
Five-membered cyclic , -unsaturated ketones	214
, -Unsaturated carboxylic acids and esters	195
Increments (in nm) for
Double bond extending conjugation:
Heteroannular	30
Homoannular	69
Alkyl group or ring residue:
	10
	12
,	18
Polar groups:
9OH
	35
	30
	50
9O9CO9CH3 and 9O9CO9C6H5: , , ,	6
9OCH3	35
	30
	17
	31
9S9alkyl,	85
9Cl
	15
	12
9Br
	25
	30
9N(alkyl)2,	95
Exocyclic double bond	5
Solvent correction (see Table 7.13)
Calculated wavelength	total