Ebook A Handbook of spectroscopic data chemistry Part 1

A Handbook of
Spectroscopic Data

CHEMISTRY
(UV, JR, PMR, JJCNMR and Mass Spectroscopy)

B.D. Mistry
B.K.M. Science College.
Va/sad - (Gujarat)

Oxford Book Company
Jaipur, India


ISBN: 978-81-89473-86-0
Edition 2009

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Contents

1.

Ultraviolet Spectroscopy

2. Infrared Spectroscopy
3. Proton Magnetic Resonance Spectroscopy
4. Be NMR Spectroscopy
5.

Mass Spectrometry

6.

Structural Data Obtainable from Different Spectra

Index

1
26
64
99
128
237
240


"This page is Intentionally Left Blank"


1

Ultraviolet Spectroscopy

1.1

Calculating Absorption Maxima of Unsaturated Compounds
Dienes and trienes : If the compound is suspected to be a conjugated

or substituted diene, its wavelength of maximum absorption can be predicted
with the help of Table I. I. To be able to use this table, one must first learn to
recognize different types of dienes, conjugations, double bonds, etc. These
are as follows:

c=c< _ ) C=C< A linear conjugation; for example, 1,3,5
C-C
hexatriene, isoprene,etc.
) C=C<
A cross conjugation.
ii) )C=C
)C=C<
i) )

iii)

iv)

o
o

A cyclic diene; for example, cyclohexadiene,

cyclohepta 1,3- diene, etc.
A semicyclic diene; one of the double bonds
forms part of a ring and the other is
exocyclic, or outside the ring. When only
one of of the two Sp2 hybridized carbons of
a double bond is a part of the ring under


2

Spectroscopic Data Chemistry
consideration, such a double bond is called

an exocycIic double bond.
A homoannular diene is one in which the

v)

two double bonds are conjugated and are in
a single ring.
Note that both double bonds are
exocycIic to ring B.
vi)

A heteroannular diene is a conjugated system
in which the two double bonds belong to two
different rings. However, these double bonds
are also exocycIic, one of them being exoto ring A and the other exo-to ring B.

Table 1.1: Woodward's and Fieser's rules for Diene absorption (ethanol
solution)
i)

Base value for an unsubstituted, conjugated, acyclic or
heteroannular diene

ii)

214 nm

Base value for an unsubstituted, conjugated
homoannular diene

253 nm

Increments for
iii) Extra double bonds in conjugation (for each C=C)

+30 nm

iv) ExocycIic double bond (effect is two fold ifbond is
exocylic to two rings)
v)

+5nm

Substitutents on Sp2 hybridised carbon atom, per substituent
a) O-acyl (-O-CO-R or -O-CO-Ar)

Onm

b) Simple alkyl (-R) or ring residue

+5nm

c) Halogen (-CI, -Br)

+5nm

d) O-alkyl (-OR)

+6nm

e) S-alkyl (-SR)

+30nm

f) N-alkyl, (-NRR ')

+ 60 nm

vi) Solvent correction

Onm


3

Ultraviolet Spectroscopy
,

The following points are to be noted:
•

The cyclic homoannular base values refer to a six membered ring
only. For other rings the values are:
Five membered ring (C s)

228 nm

Seven membered ring (C 7 )

241 nm

•

Accuracy of prediction is ± 5 nm

•

If there is more than one possibility for calculating Amax, the highest
Amax value usually agrees with the observed value.

Limitations
•

Agreement is quite good for acyclic and six-membered ring polyenes
but not so for other rings in some cases.

•

Steric strain can also affect the position (Amax) of the band,
sometimes very greatly if the strain is high. A simple example of
this is 1,2 dimethylene cyclohexane, which gives a strong UV band
at Amax 220 nm (E 10,050) which is quite different from the
calcualted value.

Polyenes : The above rules (Table 1.1) holds fairly well for unsaturated
compounds containing up to four conjugated double bonds. However, for
systems of extended conjugation, such as those found in carotenoid pigments,
Fieser and Kuhn have suggested equations to calculate the basic Amax and
Em.. ofUV absorption.
Amax (in hexane) = 114 + 5M + n (48.0 - 1.7n) -I 6. 5Rendo - IOR exo

E ma , (in hexane)

=

1.74 x 104n

Where
n = number of conjugated double bonds
M = number of alkyl or alkyl like substituents on the conjugated system.
Rendo = number of rings with endocyclic double bonds in the conjugated system.
Rexo =

1.2

number of rings with exocyclic double bonds.
Calculating Absorption Maxima of Carbonyl Compounds
The basic chromophore containing a >C=C< (--ene) conjugated with a

>c=o (-one), as in


4

Spectroscopic Data Chemistry
P

a

> C = C- C = 0

.
IS

called an enone. If a carbonyl group is conjugated

with two double bonds (-cliene), such as
Ii
y
P a
>C=C-C = C-C = 0
The compound is known as a dienone. In the case of cyclic compounds,
the ethylenic double bonds conjugated with the carbonyl may be homoannular
or heteroannular.

Table 1.2: Rules of Enone and Dienone absorption

P-

paZ

0

y

paZ

I

I

I

I

I

I

I

I

C = C - C = 0 and 0 - C = C - C = C - C = 0
Enone
Dienone
Z = C, enone, Z = H, aldehyde
Z = OH, acid, Z = OR, ester

Parent enone (acyclic or rings larger than 5 members)
5-membered cyclic enone
Aldehydes
Acid and Esters
Increments for Double bond extending conjugation (for eacb one)
Homodiene component
Exocyclic double bond (or any >C=C< endocyclic to 5- or 7member ring in a case of acid and ester)
Alkyl group, ring residue
a

p

215nm
205nm
210nm
195nm
+30nm
+39nm
+5nm
+IOnm
+12nm

y
Hydroxyl (-OH)

Alkoxyl (-OCH 3)

and higher

+ISnm

a

+35nm

p

+30nm

y
a
y

50nm
+35nm
+30nm
+ 17nm

o

31nm

p


5

Ultraviolet Spectroscopy
Acetoxyl (-O-COCH 3 )
Dialkyl aniino (-NR)
Chlorine (-CI)

a, ~ or <')

f

~
a

+ 15nm
+12nm

+ 85nm
+ 25nm

Thioalkyl (-SR)
Bromine (-Br)

6nm

+ 95nm

a

~
Solvent correction (see table below)

+30nm
variable

Solvent Corrections (Enones)
Solvent
Ethanol
Methanol
Water
Chloroform
Dioxane
Ether
Hexane
Cyclohexane

Correction

o
o
-8 nm
+ I nm
+5 nm
+7nm

+ 11 nm
+ II run

Accuracy of prediction ± 5 nm.
1.3

Calculating Absorption Maxima of Aromatic Molecules

There are two types of aromatic molecules: benzenoid and
nonbenzenoid. Their spectra show considerable resemblance. In fact, the
presence or absence of certain features in UV spectra, such as a low intensity
band (known as a fine structure band) at or about 255 run, is often used to
detect the aromatic character of an unknown substance.
Benzene Chromophore
The simplest aromatic compound is benzene. It has a ring current of 1t
electrons, which shows strong 1t ~ 1t* absorptions at 184 run (Em" 60,000),
and at 204 nm (Emax 7900). (This is called a primary band.) Benzene exhibits
a low intensity band at 256 nm (Emax 200) (Known as a secondary or finestructure band), with a series offine-structue bands between 230 and 270 nm).
Any substitution ~ the benzene ring, irrespective of its electronic character


6

Spectroscopic Data Chemistry

(electron-donating or electron-withdrawing character) shift the primary band

(204 nm) to longer wave lengths. With polar substituents, e.g.
etc. which allow for the n

~ 1t

-N~,

-OH,

conjugation and -C = 0 and -N0 2 where

polarisability is of importance, absorption due to electron transfer transitions
is apparent. These two types of transfer can be expressed as shown below:

Chromophore substitutents:

Auxochrome substituents:

Table 1.3: Scotts rules for calculation ofAmax ofthe ET (electron transfer)
band of aromatic carbonyl compounds
Ar-C-Z

II

o

Parent chromophore : Ar=C6HS
Z = Alkyl or ring residue, (e.g.; ArCOR) 246 run
250 run
Z = H, (Ar CHO)
Z = OH, OAlk, (ArCOOH and ArCOOR) 230 run
Increment for each substitutent on Ar:
- Alkyl or ring residue
0-, m+3 nm
p+ 10 nm
- OH, -OAlk
+7 run
0-, m+25 run
p-- 0- (oxyanion) •
+Ilnm
o+20 run
m+ 78 run"
p-

In heterocyclic chemistry
model compounds are
essential for the interpretation of most spectra.
No rules are available for
the predicition ofthe wavelength maxima ofaromatic
compounds except in the
case of aromatic carbonyl
compounds where acetophenone is taken as the
parent chromophore, and
increments allotted on the
usual basis (Table 1.3)

7

Ultraviolet Spectroscopy

--

CI

0--,

m-

+0 mn

p-

+ 10 nm

-

Br

0--,

m-

-

-

NH2
NHCOCH 3

t

2 nm

p-

+ 15 nm

o-,m-

+I3nm

p-

+ 58 nm

o-,m-

+20nm
+45nm

-

NHCH 3

pp-

-

N(CH 3)2

o-,m-

+20nm

p-

+ 85 nm

+ 73 nm

"This value may be decreased markedly by steric hindrance to coplanarity.
Let us now apply the rules in Table 1.1, 1.2, and 1.3 to a few known
compounds and compare the resulting values of Amax with the values observed
experimentally.
I. Dienes
(1) Abietic acid

Basic heteroannular diene

214nm

Exocyclic double bonds (1 x 5)

05nm

Substituents R (4

20nm

x

5)

Calculated Amax

239nm

Observed

241 nm

[Chromophore is shown by heavy lines; numbers indicate substituents.]


Spectroscopic Data Chemistry

8
(2) Ergosterol

HO
253 nm

Basic homoannular diene
Exocyclic double bonds (2 x 5)

lOnm

Substituents R (4 x 5)

20nm

Calculated "'-max

283 nm

Observed

282 nm

3.3, j3-Acetoxyergosta-5,7,14,22-tetraene
4

In compounds containing both
homoannular and heteroannular double
bonds, the diene system which requires
least energy for excitation (i.e. the one
with the longer wavelength of absorption)
is used as a base.
253 nm
15 nm
25nm
30nm

Basic homoannular diene
Exocyclic double bonds (3 x 5)

Substituents R (5 x 5)
Extra double bond in conjugation

323 nm
319nm

Calculated "'-max
Observed
II. Polyenes
(1) All trans j3-carotene

Me

Me
Me
Me

Me


Ultraviolet Spectroscopy

9

Basic Amax value

114 nm

M

= number of alkyl substituents, 5 x 10 add

50 nm

n = number of conjugated double bonds,

11

x

[48-(1.7

x

11)]

add

322.3 nm

Rendo = number of rings with endocyclic double bonds,
2 x 16.5, substract
Rexo

= number of rings with exocyclic double bonds,

ox

Emax

33.0 nm

10, substract

00.0 nm

Calculated Amax

453.30 nm

Observed

452.00 nm

=

1.74 x 11 x 104

= I 9.1 x 104 (calculated)
=

*

15.2 x 10 4 (observed*)

The equation for calculating

Emax

is semi-empirical, the value calculated

does not always correspond well with the observed value.
(2) All trans Iycopene

114 nm

Basic Amax

M=5 x 8

add

40nm

n= 11 x 148-(1.7 xII)

add

322.3 nm

(Note: Double bonds at ends are not in conjugation with others)

E

max

= 1.74

substract

00.0 nm

substract

00.0 nm

Calculated Amax

476.30 nm

Observed

474.00 nm

x II x 104

= 19.1 x 104 (calculated)

= 18.6

x 104 (observed)


10

Spectroscopic Data Chemistry

III. Enones
(1) Cholest--4-en-3-0ne

Parent base
Subst::iJ:uents~, ~

(2 x 12) add
Exocyclic = C< add

215 nm
24 nm
05nm

Calculated AEtOH
max

244nm

Observed

241 nm

(2) Cholesta-2,4-dien-()....{)ne

Parent base
Extended conjugation
Homoannular component
Substituents a. (l x 10)
8 (l x 18)

(3) 3,

215 nm

add
add
add
add

30nm
39nm

10 nm
18 nm

Calculated AEtOH
max

312 nm

Observed

314 nm

~-Acetoxy-7-()xolanosta-5,18,11-triene


11

Ultraviolet Spectroscopy

215 nm

Parent base

Extended conjugation

add

30 nm

Homoannular component

add

39 nm

Exocyclic double bond

add

5nm

Substituents a(l)( 10)

add

10nm

12)

add

12 nm

0(\ x 18)

add

18 nm

~ (\ x

Calculated A. EtOH
max

329 nm

Observed

327 nm

(4) Cycloheptene-l--carboxylic acid
a

0

II

ot~H
IK. p
Parent base
Substituents a(l x lO)

add

IOnm

~(lxI2)

add

12 om

add

05 nm

C=C endocyclic to 7-member ring,
Calculated A. EtOH
max

195 nm

222 nm

(5) 3-MethyI-2-butenoic acid
CH 3

H

I

I

CH 3-C = C-COOH

t

t

~

a

Parent base

195 nm

Substituents a (l x 10)
~(l x

10 nm

12)

12 nm

Calculated

217 nm

Observed value

216 nm

12

Spectroscopic Data Chemistry

Dicarbonyl compounds

Diosphenol
215 run

Parent base
2~

Substituents

(2 x 12)

24 run

a-OH (1 x 35)
Calculated

35 run

AEtOH
max

274 run

Observed AEtOH
max

270nm

In cyclic a-diketones, the enolic form is generally more stable than the
keto foml and therefore, the absorption is related to that of an a, 13-unsaturated
carbonyl system. Six-membered cyclic a-diketone known generally as
diosphenols, exist in solution largely in the enolised form. In strong alkaline
solution the absorption shifts to about 50 nm to longer waves, due to the
formation of the enolate ion, to enable diosphenol structures to be characterised.
Acetyl acetone exists in the enolic form to the extent of about 90% in
solution in non-polar solvents and the absorption directly depends on the
concentration of the enol tautomer.

..' H ""

o

0

0

II

II

II

CH -C

J

<

C·CH

'"

/

J

,

a~-diketone

Isoo ctane 272

,

274,

C.CH.

-'"

CH

Acetyl acetone

1

I

>CH.--C

CH 2

"'rna,,;

0

Ema~ 12,000
E

max

2050

-f"

'


Ultraviolet Spectroscopy

13

However, in the case of acetyl acetone agreement with the calculated
wavelength (257 nm) is indifferent. This may be due to the fact that the strong

internal hydrogen bond forces the carbonyl group and the double bond into a
configuration different from that which is present in cyclic structures, e.g.,
diosphenol exists almost entirely in the enolic form.
1,3-cyclohexanedione, absorbs at 253 nm

(Emax

22,000) in ethanol

O~OH

O~O

V<-->~ -V
1,3-Cyclohexanedione

The formation of enolate ion in alkaline solution in these cases also
shifts the strong absorption band. Quinones represent a-, or vinylogous adiketones. The spectrum of p-benzoquinone is thus found to be similar with
that of a typical a, f)-unsaturated ketone with the strong K-band appearing at
242 nrn and a weak R-band near 434 nm.
A.~:ne = 242 nrn (E 24,000)

6

(7t ~ 7t*

K-band)

281 nrn (E 400)} n ~ 7t *
434 run (E 20) R - band

o

The colour of the simpler members is due to the weak n ~ 7t* transition
which is also present in a-diketones. The n ~ 7t* transitions of a-diketones in
the diketo form gives rise to two bands one in the usual region near 290 nm
(E

~

30) and a second (E 10 ~ 30) which stretches into the visible 340--440 nm

region to give yellow colour to some of these compounds.

IV. Aromatic carbonyl compounds

o
II

1.

I -. . . :

HO"'-.cr

/
HO

~

C

Base value
"-. CH

246nm

OHinm

07 nm

OH inp

25 nm

3

278 nrn


14

Spectroscopic Data Chemistry

0

2.

Base value

00

(CH,),NO
H,NO

Brin m
-CH 2 in 0

246nm
02nm
03 nm
251 nm

Br

3.

~

4.

I~

Base value

250nm

NMe 2 inp

85nm

335 nm

CHO
Base value

230nm

NH2 in p

58nm
288nm

COOH

Another approach to predicting, the "-max of the primary band of
substituted benzenes involves the use ofTable 1.5. This table has been successfully
used with disubstituted compounds when the following rules are used:
I. Para substitution:

a.

b.

Both groups are either electron donating or electron withdrawing:
Only the effect of the group causing the larger shift is used. For
example, the "-max ofp-nitrobenzoic acid would be expected to be
the same as that of nitrobenzene, -(203.5 + 65.0) = -268.5 (in
alcohol solvent).
One group is electron donating and the other electron withdrawing:
The shift in the primary band of such a disubstituted benzene is

usually greater than the sum ofthe shifts caused individually by the
two groups. Such large shifts in p-disubstituted benzens are
attributed to interaction resonance, as illustrated below:


15

Ultraviolet Spectroscopy

2. Ortho and Meta substitution: The shift effects are additive.
Table 1.4: Absorption characteristics of some polycyclic aromatic
compounds
Compound

Amax,

emax

nm

Amax, emax

nm

Amax, emax

nm

CD

184

47,000

203

7,400

255

230

ro

220

1,10,000

275

5,600

314

316

OGCJ

252

2,00,000

375

7,900

252

50,000

295

13,000

330

250

240

89,000

334

50,000

352

6(30

268

1,41,000

320

13,000

360

630

278

1,30,000

473

11,000

580

12,600

Benzene
:::-..

/-

Napthalene

:::-..
//Anthracene

~
I"
/-

Phenanthrene

m
~ I/-

Pyrene

Chrysene

OXO
:::-..

/-/-/-

Napthacene

:::-..
~
/-/-/-/-

Pentacene

• These weak bands are usually submerged by strong adjacent bands .

16

Spectroscopic Data Chemistry
~

Table 1.5: Calculation of the Primary Band (1[
substituted Benzenes (CH 30H solvent)
Base Value: 203. 5 nm

1[*Transition) of

Substitutent

Shift

Substituent

Shift

-C H3
-CN
-CHO
-COCH3
-COOH
-Br
-CI

3.0

20.5
46.0
42.0
25.5
6.5
6.0

-NH2
-NHCOCK
-N02

26.5
38.5
65.0
7.0
31.5
13.5

J

-OH
-0-OCH 3

Absorption Characteristics of Disubstituted Benzens:
1[
Compound

o-N0 2 Phenol
m-N0 2 Phenol
p-N0 2 Phenol

o-N0 2 Aniline
m-N0 2 Aniline
p-NO? Aniline

~

1[*

Transition
KBand
Amax (nm)
Emax
279
6,600
274
6,000
318
10,000
283
5,400
280
4,800
381
13,500

BBand
Amax (nm)
Emax
3,200
351

333
1.960
Submerged
412
4,500
358
1,450
Submerged

Table 1.6: Absorption characteristics of Aromatic systems and their
substituted derivatives
Compound

Solvent

Primary band
1[ ~ 1[*
Transition
KBand

Amax

E

rna,

(nm)
Benzene
Toluene
o-Xylene

Hexane
204
Methanol(2%) 206.5
Methanol
210

1[

Secondary band
1[*
n ~ 1[*

~

Transition
BBand

Transition
RBand

Amax

Amax

E

max

(nm)

7,900
7,000
8,300

256
261
263

(nm)
200
225
300

E max


17

Ultraviolet Spectroscopy
Compound

Solvent

Primary band
1t ~ 1t*

Transition
KBand
Amax

Emax

(nm)

Secondary band
n ~ 1t*
Transition
Transition
RBand
BBand
1t .~ 1[*

A

A

Emax

max

max

Emax

(nm)

(nm)

m-Xylene

Methanol

212

7,200

265

300

p-Xylene

Methanol

212

8,000

274

460

244

15,000

280

1500

328

20

Acetophenone Ethanol

240

13,000

278

1,100

319

50

Benzophenone Ethanol

252

20,000

325

180

Nitrobenzene

Hexane

252

10,000

280

1,000

330

125

Benzonitrile

Water

224

13,000

271

1,000

Alcohol

232

14,000

262 2,400

sylfone

Alcohol

217

6,700

Biphenyl

Alcohol

246

20,000

Benzaidehyde Ethanol

Diphenyl
Sulfoxide
Methyl phenyl

2,2'-Dimethyl

264

977
Submerged

222

270

800

methane
Ethanol
Styrene
Hexane
Phenylacetylene

500

244
236

12,000
12,500

262
282
278

Stilbene (cis)

Alcohol

283

12,300

Submerged

Stilbene (trans) Alcohol

295

25,000

Submerged

Cinnamic acid (cis)

268

10,700

(trans)

272

15,900

biphenyl
Diphenyl-

-

1-Pheny I-I ,3butadiene (cis) Isooctane

268

18,500

(trans) Isooctane
1,3-Pentadiene

280

27,000

223
223.5

22,600

(cis) Alcohol
(trans) Alcohol

23,000

450
650


18

Spectroscopic Data Chemistry

Compound

Solvent

Primary band

n

~

n*

Transition
KBand
Amax
E
max
(nm)

Secondary band
n*
n ~ n*
Transition
Transition
BBand
RBand
Amax E m.. Amax E rna<

(nm)
(nm)

n

~

Chlorobenzene Ethanol

210

7,600

265

240

Thiophenol

236

10,000

269

Methanol (2%) 217
Anisole
210.5
Phenol
Water

Phenolate anion Alkali (aq)
235
Water (P H3)
214
o-Catechol
o-Catecho late Water (PHIl) 236.5

6,400
6,200

269
270

700
1,480

Hexane

9,400
6,300

1,450
287 2,600
276 2,300

6,800

292 3,500

8,600

7,500

280

1,430

254

160

anion
Aniline
Water
AniliniumcationAcid (aq)
Acetanilide
Water

230
203
238

Diphenyl ether Cyclohexane

255
275
375
474

Naphthalene
Anthracene

Tetracene
(Napthacene)
Pentacene
Pyridine

Ethanol
Hexane

Quinoline

Cyclohexane

lsoquinoline

Cyclohexane
Ethanol

Acridine

Ethanol
Ethanol
Ethanol

580
257
270
265

10,500
11,000

272 2,000

5,700
8,000
13,000

312

250

270

450

15,000
2,750
3,161

358

4,170
10,000
Band I
10,000

Furan

Cyclohexane

200

Pyrrole
Thiophene
Pyrazole

Hexane
Hexane
Ethanol

209
231
214

315 2,500
313

1,800
Band II

252

I"

6,730 240
7,100 269.5

300"
1.5"

3,160

These weak bands may be due to impurities rather than a forbidden
transition (n

~

n*) ofa hetero aromatic molecule.


19

Ultraviolet Spectroscopy

Spectra of nonbenzenoid aromatic hydrocarbons show considerable
resemblance to spectra ofbenzenoid compounds, Tropolone and its derivatives
show absorption in the region 220 - 250 nm (

Emax

ca 30,000) and 340 - 375

nm (Emax ca 8,000); the latter absorption is characterized by the group of fine
structure bands typical of aromatic systems.

Q
HO

tropolone

0

Azulene and its derivatives have complicated spectra consisting of a
number of relatively intense bands throughout most of the ultraviolet region
(up to 360 nm) and a number of relatively weak bands throughout most ofthe
visible region (500 - 700 nm). As a consequence of the latter, azulene and
most of its derivatives are blue.

azulene

1.4: Approximate lower cutoff wavelengths* for commonly used solvents
in UV-visible spectroscopy of organic substances
Solvent

Cutoff

Solvent

wavelength, nm

Cutoff
wavelength, nm

200-250

250-300

Acetonitrile

2\0

Benzene

280

n-Butanol

210

Carbon tetrachloride

265

Chloroform

245

N,N-Dimethylformamide

270

Cyclohexane

210

Methyl formate

260

Decahydronapthalene

200

Tetrach loroethy lene

290

1, I-Dichloroethane

235

Xylene

295

Dich loromethane

235


20

Spectroscopic Data Chemistry

Solvent

Cutoff

Solvent

wavelength, nm
Dioxane

225

Dodecane

200

Ethanol

210

Ethyl ether
Heptane

300-350
Acetone

330

210

Benzonitrile

300

210

Bromofon-n

335

Pyridine

305

Hexane

210

Methanol

215

Methylcyclohexane

210

isooctane

210

isopropanol

215

Water

210

*

Cutoff
wavelength, nm

350-400

Nitromethane

380

Cutoff wavelengths: i.e. useful wavelength range is beyond the indicated
wavelength.

Exercises and problems:
(1) Explain the differences in the electron spectra of compounds (2) and
(3) compared to compound (1)
I.

(CH 3)2 N-Q-N = N-Q-N0 2
"-max = 475, E = 32,000

2.

= N~
~ NO
(CH.)
, 2N-~N
)=/

2
CH 3
"-max = 438, E = 22,000

....

.).

(CH 3)2 N-p-N = N-o-N0 2
HC(CH 3)2
"-max = 420, E = 18,600

(2) Identify which one of the following two isomers has the electronic
absorption band with "-max = 241 nm and Emax = 18000