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[CONTRIBUTIONROM

THE

GEORGE ERBERT ONESCHEMICALABORATORY,H E

UNIVERSITY

F

CHICAGO]

SOME RELATIONS O F CARBON AND ITS COMPOUNDS*

WILLIAM

D.

HARKI NS

Received February

9, 1956

1. INTRODUCTION

The purpose of this paper is to present a few topics, related to organic

chemistry, which have come, more or less intimately, into the work

of

the

author. This has involved the following subjects related to carbon and its

compounds:

(1)

the nuclear chemistry of carbon,

(2)

free radicals

of

short

life and the organic chemistry of electrical discharges, (3) the synthesis of

dyes and explosives, (4) plastics, and (5) the applications of surface

chemistry in organic chemistry, and of organic chemistry in surface

chemistry.

From these the first, second, and fifth topics have been chosen as illus-

trating best the applications

of

physical chemistry.

2 .

NUCLEUS O F

THE

CARBON ATOM

Carbon is element six in the periodic system of the electronic region of

the atoms, and also in the very different periodic system

of

atomic nuclei.

From the standpoint of theory this is expressed by the statement that

there are six negative electrons in the non-nuclear, presumably outer,

part

of

the atom, and an equal, but positive charge, on the nucleus, or

massive part,

of

the atom. Since neutrons are without any outer elec-

tronic system, and thus consist of non-charged atomic nuclei, the element,

neutron, is designated by the atomic number, zero. Thus carbon is now

the seventh element of the system, but with the number six.

Carbon contains two known stable isotopes: about 99.3% of isotopic

number zero and atomic mass 12.0035 f 0.0003 together with about 0.077,

of isotopic number 1, and atomic mass 13.0073. In addition there isa radio-

active isotope of mass 11.0143, formed by the reaction of a proton with

boron

of

mass

11.0128

and the release

of

a neutron, or

of

a deuteron on

boron of mass

10, with release of a neutron. The radioactive isotope

liberates a positive electron and changes into boron

of

mass 11.0128.

This paper was submit ted in response t o th e invi ta t io n of t he Ed i to r s .

52

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RELATIONS OF

CARBON AND

ITS COMPOUNDS 53

T:he nucleus of the ordinary carbon atom of mass

12.0035

may be con-

sidered to consist of six neutrons and six protons. These are arranged in

t,he :form

of

3

alpha particles or helium nuclei, which however, lose

a

part

of

their identity. This nucleus

is

one

of

the most stable

of

known nuclei,

TABLE

I

O R G A N IC O M P O U N D S

ISOTOPICOMPOSITIONF ELEM ENTS

HOSE

A T U R A L

SOTOPES

RE FOUNDN

h ote:

Bromine isotopes

of

half-periods

18

minutes , 4.2 hours , and 30 hours have

been described.

in the sense that i t does not readily undergo

a

nuclear reaction. However,

it reacts with deuterium (H2) to give a neutron and a radioactive species

of

nitrogen (N*13)as follows:

' 12

:H2 N 4 --j

-iN 13

1

On

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54 W I LLI AM D. HAR KI NS

This disintegrates, with a half period of 10.5 minutes, to give a positive

electron and carbon of mass 13.

- 1 ~ 1 3 + 1 C l 3

+-‘E+

7

Here the subscript is the atomic number (2) and the superscripts are

the isotopic number I ) and the atomic mass M ) . The general formula

of any nucleus is (np),n, in which n is a neutron and p

a

proton.

The values, 2 =

6,

I = 0, designate the ordinary carbon isotope of mass

twelve, while 2 = 6, I = 1 epresents the less abundant isotope of mass 13.

These isotopes differ only very slightly in their chemical properties.

The isotopic composition of a number of elements common in organic

compounds is listed in Table

I.

3. I SOTOPI C OR GANI C MOLEC ULES

Since there are two stable isotopes of carbon and three of hydrogen the

number of isotopes of organic molecules is very large. Thus for even so

simple a compound as methane there are 30 isotopes, though only 10 if

merely protium and deuterium are considered. There are 537 isotopes of

hexane, or 91 for the two most abundant hydrogen isotopes. The corre-

sponding numbers for benzene are 196 or 49, and for dichloroethane 120

or 45.

If

there are e elements in the compound molecules, and

n

atoms of any

element, and

i

isotopes of the element, then the number of molecular

isotopes is given by the formula of Mulliken and Harkins as:

(n’

+

’

- )

n”

+ i” - ) n”’ i”’ - l )

ne

+

e - )

n ’ n ” n ” ’ . . .

ne

( i t

-

I)

it’-

) i t ’ ’ - I) . . e- )

This does not include isomerism. It is evident that the number of

isomeric-isotopes is extremely large except in the simpler organic molecules.

New optical isomers are possible as a result of isotopism in

so

far as

differences

of

mass and nuclear spin are able to make the molecule asym-

metric.

4. T H E O R G A N I C C H E M I S T R Y O F E L E C T R I C A L D I S C H A R G E S A N D

E L E C T R O N B E A M S

By the use of electrical discharges of various types through organic

vapors, or of electron beams through vapors, liquids, or solids, it is possible

to obtain organic reactions of varied types.

Thus, with electrodeless discharges of

600

kilocycles frequency, it was

found that one thousand liters of benzene vapor per hour a t 0.25 mm.

pressure could be decomposed and resynthesized in a one-liter flask. The

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RELATIONS O F CARBON AND ITS COMPOUNDS 55

product is a reddish-brown solid, insoluble in organic solvents, and evi-

dently of very high molecular weight, with exactly the same elementary

composition as benzene (CH),.

The spectrum of an electrodeless or glow discharge or an electron beam

through an organic vapor exhibits a number of emission bands which reveal

the presence of diatomic molecules of abnormal valence. Thus, if the

organic vapor is a hydrocarbon, molecules, or free radicals

of

short life,

of methine or monohydrocarbon (CH), and dicarbon

(C,),

are revealed,

together with free atoms of carbon (C), and of hydrogen

(H),

together

with positive ions of carbon (C+). While the spectrum does not reveal

them, both dissociated and ionized forms of the initial organic molecules

are also present. Such a gaseous mixture is extremely reactive as is made

evideint by the experiment with benzene vapor.

If oxygen is present, hydroxyl bands and carbon monoxide bands reveal

the presence of these molecules, ( OH and CO) and water separates

as

such, while with nitrogen, inimine

(NH),

and cyanogen (CN) radicals

appear, together with Nz and

N t .

The changes outlined above represent the dissociation of the organic

molecules into fragments which are free radicals, atomic or molecular ions,

and uncharged atoms.

If the frequency of the electrodeless discharge is increased, the energy

lessened, or with electron beams, if the velocity is sufficiently decreased,

much, milder changes may be induced.

Thus

it

seems that by electron collisions an electron, a proton,

a

methyl

group, etc. may be removed from a molecule and leave the remainder of

the molecule unchanged in composition. In some instances the composi-

tion of the whole molecule is not changed but

a

double bond is shifted

from one position to another.

The energy of an electron which could excite a wave-length of 3000

is

6.55

X ergs or 4.12 electron volts (e.v.) per photon. At

2600

i

the energy would be 4.75 e.v.

The action of electrons on molecules is much less specific than that of a

particular wave-length of light. The moving electrons can affect many

more electrons in the molecule, and their action is more specifically upon

the electrons in the molecule than upon the molecule as a whole, but they

may incite a rearrangement of the atoms in the molecule, and it seems

that they are efficient in the production of dissociation.

Positive or negative ions produced in the discharge have in impacts a

more specific action on the atoms than on the electrons. They possess

a

potential energy different from tha t of the neutral atoms, and may give

off or receive energy on this account. Ions may affect electronic motions

in rrtolecules which they strike but with

a

very much smaller efficiency

than electrons.

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56

WILLIAM

D.

HARKINS

The chemical effects of electrodeless and glow discharges between elec-

trodes are different in many respects. Thus benzene in a glow discharge

polymerized rapidly to give a white deposit, probably dihydrodiphenyl,

approximately 10 molecules of benzene being removed by each equivalent

of current. This can be accounted for by a chain mechanism initiated

by radicals formed in an amount proportional to the current, although it

is not improbable that some of the faster electrons formed more than one

radical.

Brewer and Kueckl find that ethylene is quantitatively converted into

methane and hydrogen in a

D.C.

glow discharge when the tube is immersed

in liquid air. They consider the reaction to be

CH$

+

CH,

C,Ht

+

2H2

and that the ethylene ion is subsequently neutralized in a wall reaction.

In the electrodeless discharge there are two electrical fields, one an

alternating electrical field, parallel to the axis of the solenoid, and the

other an electromagnetic field whose electrical energy is in rings perpen-

dicular to the axis of the solenoid. Both fields may play a part in the

discharge reaction, but the electromagnetic field must be most important

in the initial ring discharge, and the electrostatic field parallel to the axis

most important in the glow which comes later. The pulsating D. C. elec-

trostatic field between the electrodes in the glow discharge

is

comparable

to the field responsible for the glow in the electrodeless discharge.

The differences between the reactions in the two discharges, which are

shown by differences in their spectra and products, must depend on the

differences in pressure and electrical fields. For instance, it is conceivable

that more collisions favorable for the combination of hydrogen atoms into

molecules take place at the higher pressure in the glow discharge than in

the electrodeless discharge, thus accounting for the appearance of the

many-line spectrum of hydrogen in the glow discharge. The Baldet-

Johnson high-pressure bands of CO+ may appear in the one rather than

the other, not only on account of the difference of pressure but also be-

cause of a difference in electron energy, since energies of the order of one

hundred electron volts are required for the appearance of these bands.

Tables I1 and I11 give the colors of the discharges and of the solid

products for certain electrodeless and glow discharges.

Since many of the intermediate products in electrical discharges are

free radicals of short life, the discussion

will

be continued under this topic.

f BREWER

ND

KUECK,J . Phys .

Chem.,

36, 1293 (1931).

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R E L A T I O N S O F C AR B ON A N D

ITS COMPOUNDS 57

5. F R E E R A D I CA L S O F S H O R T LIFE

Free radicals were defined by Wieland2 in 1915 as atomic complexes of

abnormal valency which have additive properties, but do not carry an

electrical charge and are therefore not free ions.

Most free radicals, which are considered in discussions of the subject,

possesii one unsatisfied valency.

“In chemistry

it

is customary to call a structure a free radical only when

it saturates its valences with energies of the order of magnitude of that

of an ordinary chemical rea~t ion.”~

Schlenk4 considers molecules which contain an odd number of electrons

(odd molecules) as free radicals. Such a definition is, on the whole, a

good one, but there are exceptions such as the CHZ radical, which may be

an “even” molecule, found by positive ray methods.

Also

many chemists

dislike to class odd molecules such as NO,

NOz,

ClOz, HzP03, as free

radicals.

The latter definition, however, suggests one of the most important physi-

cal methods which may be used in the study of the nature of sufficiently

stable free radicals; that is, a determination of the magnetic susceptibility

of the material.

The molecular mass susceptibility of a substance, which is not ferro-

magnetic, may be expressed as the sum of three terms:

x

=

X d

+

x p

+

X r r

where

X d

is the diamagnetic portion due to the disturbance of the electron

orbits by the field, and ranges from

- .88

X lo5 or helium to a negative

value of

a

few hundred units for substances which consist of complex

organic molecules. For organic molecules in general

x

is zero, and

x

is small, so xpZxXdd

In the case of odd molecules, however, the molecule possesses a perma-

nent magnetic moment

I.

which gives rise to a large positive term x

which accompanies paramagnetism. The magnetic moment is deter-

mined by the resultant angular momentum of all of the electrons.

It

has

been shown5 that

x

is determined mostly by the net spin S of the mole-

cule, and that the approximate relation

is

X S + 1)

T

p

= 1.242

X l o 5

2 WIELAND,Ber.,

48

1098 (1915).

3 K. STEINER,Free Radicals,

a

General Discussion.” T he Fara day Society,

4

SCHLENK, 4th. Cons. Chim. Solvay,” 1931, p. 503.

5 VAN VLECK,“The Theory of Electric and Magnetic Susceptibilities.”

1933, p. 39.

Oxford

Univers i ty

Press,

1932.

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58

WILLIAM D.

HA R KI N S

a-Naphthlydiphenylmethyl . . . . . . .

{

Potass ium benzophenone . . . . . . . . . . . .

Potass ium

phenyl-p-biphenylketone..

. .

CisHz102Nz. . . . . . . . . . . . .

.

. . . . . . . . . .

In an odd molecule, if only one electron is unbalanced, S = 3 and at

20°C. the value of

x r

is +1270, which is much larger than

x d

and of the

opposite sign. From

(1)

xr should vary inversely as the absolute tem-

perature as is specified by Curie’s law.

The values of

xt

for a few substances, whose molecules are free radicals,

are shown in Table

11.

Methine, or monohydrocarbon, CH.-The blue color of an electric$ dis-

charge through an organic vapor is due in part to bands at 3900 A and

4300 A found by Mulliken to be due to the neutral CH molecule with an

electronic state of the doublet type 2 I I which indicates that the emitter

has an odd electron.

The general appearance of the spectrum given by the decomposition

products of benzene in the region of the 4300 band of

CH

is shown in

20

570

I n

9”

benzene solution

17 1293 Solid

17 1109 In 20 benzene solution

24 1 5 In 15 dioxane solution

24

1080

In 17 dioxane solution

TABLE I1

VALUES F

x r

THE PARAMAGNETICERM,

N THE

MAGNETICUSCEPTIBILITYF FREE

RADICALS

N

UNITS

OF

106

SUBSTANCE STATE

/ I

Fig. 1, which exhibits the double lines characteristic of these bands, and

of hydroxyl (OH) bands also. The structure of these bands is very

beautiful.

It is assumed that the CH radical is also formed by the direct photo-

dissociation of acetylene according to the reaction :

H C = C H + h v + 2 C H

A

number of w2rkers have feound series of absorption bands in the region

between 1900 A and 2400 A which they attribute to methine.

According to a summary by Norrish,G the dissociation of the first hydro-

gen atom from CH, requires an energy of about 102 kcal., that which in-

volves the change from CH, to CH2 only 55 kcal., from CH2 CH - C,

a heat for the two steps (Mecke) of 215 kcal., while the average energy of

linkage is usually given as about 100 kcal. The accuracy of these values

is low.

6

NORRISH,“Free Radicals,

a

General Discussion.” T he Faraday Society,

1933

p. 110

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RELATIONS OF CARBON AN D ITS COMPOUNDS

59

I

1

Hydroxyl,

OH.-The hydroxyl

(OH)

molecule, in the doublet

state,

with an odd electron,

is

one of the most generally found free radicals of

short life, and occurs not only in practically all electrical discharges, where

water

is

present even in minute quantities, but also in flames in which

organic substances (or hydrogen) burn in a gas that contains oxygen. In

general the hydroxyl bands occur when an electrical discharge is passed

through an organic substance whose molecules contain oxygen, but there

is some evidence that in some such vapors a mild discharge, presumably

one in which the energy of the electrons is low, may pass without an

excitation of even the 3064 A band.

Of

all of the water bands, that at

3064 A

is by far the most prominent

and the most easily excited but others are found at 3122, 2811, 2875,

and

2808

A.

To the eye the bands, like those of

CH,

seem to consist of

double lines. Actually all three of the branches P , Q, and

R

are doubled,

and for low values of

m

the doublets are widely separated. This band ap-

FIQ.1

pears in the emission spectra of both electrical discharges and flames. Ac-

cording to Bonhoeffer and Pearson,’ the life of this radical is short (of

the order of l oF3 econds), much shorter than that of atoms of hydrogen or

oxygen. In water vapor the hydroxyl molecules seem to be removed by

the reaction

2 0 H -+ H20 +

with very little if any production of hydrogen peroxide. The reaction

is that found when hydroxyl is discharged at an anode in an aqueous solu-

tion.

Cyanogen

CN.-The cyanogen molecule is probably in the doublet

state + which indicates the presence of an odd electron. The emission

band.s given off by cyanogen are prominent in electrical discharges through

organic vapors that contain nitrogen.

Dicarbon

C2.-The dicarbon molecule is probably in the triplet state

TIpwhich indicates a valence

of

two.

The emission bands given off by C2 molecules in excited states are in

general very prominent indeed in electrical discharges through organic

1 3 O N H O E FF E R A N D P E A R S O N ,

2

h y s i k .

Chem.,

139

75 1928).

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60

WILLIAM

D

HARKINS

vapors, though, as mentioned elsewhere, certain discharges of low elec-

tronic energy give no emission bands at all that can be detected.

The decomposition spectrum of benzene often shows all five groups of

the Swan bands of Cz very prominently, while the bands of D’Azambuja

are present at X 4102, 4068, 4041, 3852, 3826, 3607, 3593, 3588, 3400, and

3398, though these are faint.

Methylene, CH2.-The methylene CHz molecule gives no emission bands.

It is

in a singlet state (‘A1) and thus has a zero valence so that it needs

to be activated in order to become reactive. Its state is similar to that

of the HzO++ ion. The first excited state of methylene is a triplet state

CBI )which indicates a valence of two.

Since methylene in the normal

state is not reactive, and is not paramagnetic,

it

is often considered that

it

should not be classed

as

a

free radical, but only

as

a

molecule.

Polyatomic

I o n s as

Revealed

by

Positive Rays.-While, in general, the

emission band spectra of organic vapors reveal no radicals more compli-

cated than those that are diatomic, possibly because these are the only

ones that are excited in sufficient quantities, the existence of more com-

plicated groups is demonstrated by the positive ray method.

Methyl, CH3, and Ethyl, CnHs.-The methyl molecule

is

probably in the

pyramidal form, and

if

so is in the doublet (2Al)state, with an odd electron,

so it should be very much more reactive than CHz.

None of these polyatomic radicals is revealed by emission spectra, but

the corresponding positive ions are formed in positive rays.

Either methyl or ethyl is formed easily by heating the appropriate lead

tetraalkyl in a stream of hydrogen or nitrogen.8*B

The half-life of the methyl radical found experimentally was 5.8 X

seconds, and that of ethyl

3.9

X

These radicals stick to metals like lead, bismuth, and zinc, and react

as follows:

Zn

+

2CH3

--f

ZII(CH~)~

Every radical which strikes a metal surface is held, but only one in a

thousand on glass or quartz. On surfaces with which methyl or ethyl do

not react, higher hydrocarbons are formed.

The positive ray parabola method as used by ConradlO with vapors of

benzene, cyclohexane, and hexane, indicates groups with 1, 2, 3 ,,4, 5, and

6 carbon at o m in each case. In benzene, four lines of about equal in-

tensity appear for

C3,

C3H, C3Hz,C3H3, while C3H4 is indicated faintly

and the higher hydrides, C3H6, C3H6, etc. are absent. With hexane and

8

F. PANETH N D W. HOFDITZ,er.,

82

1335 (1929).

9 F. PANETH

ND

W. LAUTBCH,

bid.,

64, 2702 (1931).

1 0

CONRAD,

Free Radicals,

a

General Discussion.” T he Fara day Society,

1933

p.

215.

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RELATIONS OF CARBON AND ITS COMPOUNDS 61

cyclohexane, however, the same first four lines are strong, that for C3H4

weak, but then there

is

a strong C3H5 line,

a

weak CzHs line, and finally,

in cyclohexane, two weak lines for C3H7, and C3H8, while for hexane

C3H7 s strong and C3Hs weak. Somewhat similar relations are found

for C4 nd C6.

In the case of the Cs group from hexane, Conrad assumes that the highest

mass,

71,

corresponds to a radical formed by breaking CH, from hexane, or

H H H H H

71

I I I I I

H-C-C-C-C-C-

I I I I I

H H H H H

Stable as a

positive ion

This

is

detected, however, as

a

positive ion; that is, one electron, pre-

sumably the valence electron, is missing; the binding electron is gone, and

a saturated compound has been formed. If, however, a fourth hydrogen

atom is torn out, the ion

H H H H H

70

which is also a radical, is formed.

but only a few of mass

70.

That is,

71

remains but

70

is used up.

H H H H H

Many particles of mass

71

are found,

Mass

69

appears in large quantities, which indicates stability.

Stable

69

H-C-C-C-C-Cf

H H

The two valences gained by removing two hydrogen atoms give a double

bond.

It

is

at once seen that the mass

68

is again less stable.

The relations are different with benzene, since, if the ring is broken a t

one point, no stable configuration is at first possible.

6. FREE

RADICALS OF LONG

LIFE

The general discussion of free radicals of long life will be left to the

However, a few relations will be mentioned. In therganic chemists.

molecule

/Ph

c-c

Ph/k

&>Ph

ph\

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62 WILLIAM D HARKINS

a splitting into free radicals occurs more readily if R, and R' are phenyl

than if they are ethyl groups. According to Huckel resonance of the free

electron of the radical (C6HS)3C with the double bonds of the phenyl

groups increases the stability of the radical, since, in a certain sense, the

electron disappears in the phenyl groups. According to Ziegler the size

of the substituents is extremely important. Thus, very large groups sur-

round the methyl carbon atom and keep it from uniting readily with other

radicals.

In recent years a number of organic compounds have been considered

as double radicals, on the basis of their high reactivity and intense colora-

tion. These materials exhibit a normal molecular weight instead of the

abnormal values of the ordinary free radicals.

This problem has been investigated by Muller and Muller-Rodloff"

who conclude on the basis of measurements of magnetic susceptibility

that Schlenk's hydrocarbon m,m -biphenylene-bis-(diphenylmethyl)

which cannot go over into

a

valence-tautomeric chinoid system, is a true

double radical.

At 74 the molecular magnetic susceptibility of

a

9 per cent solution in

benzol,

xmo1.

was found to be -320 20 and the difference, ~ ~ ~ l . , ~ ~ l ~ ' d

- xmol,,xp9tvl,ca. 290, which is much greater than the limit of error and

corresponds to

a

radical content of

6 2

per cent. The behavior is

entirely analogous to that of triphenylmethyl. The color of the solution

is light yellow at room temperatures, but dark orange yellow at 74 .

All of the other molecules assumed to be double radicals failed to ex-

hibit this in the magnetic effects.

These investigators consider that true double radicals can exist only if

the following conditions are fulfilled:

(1) If

there is no possibility of intramolecular stabilization, such as may

occur in other derivatives.

(2) If

there is no possibility of a change into

a

valence-tautomeric

chinoid system, as in para derivatives.

Schonberg'z believes, however, that in light the equilibrium is shifted

toward the double radical, as in solut.ions of rubrene, derivatives of an-

thracene, etc.

11

E. MULLER

ND

I. MULLER-RODLOFF,nn., 617, 144 (1935).

13

A.

S C K ~ N B E R G ,

rans.

Faraday

SOC.,

2,

514 (1936).

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RELATIONS OF CARBON AND ITS COMPOUNDS

63

DISCUSSION

The facts presented in this paper indicate that free radicals of short life

are formed in great numbers in electrical discharges of all types.

It

is

much inore difficult to regulate the discharge in such a way that large

molecules are only slightly affected, as by the removal of only one or two

hydrogen atoms, and the formation and shift of double bonds, than to

produce many diatomic radicals. In silent and semi-corona discharges,

Lind and Glockler13 found that the lower saturated hydrocarbons and

ethylene were condensed, with the liberation of hydrogen and ethane,

into products which are largely liquid, while the corona discharge yields

as much resinous as liquid product. With alpha rays, gaseous, liquid, and

solid condensation products were formed. In electrodeless discharges

solids alone may be produced with certain types of discharge.

It is often assumed (Bone, Rice, etc.) that many organic substances are

dissociated thermally in such a way as to give free radicals, which then

react, often by chain mechanisms. Rice assumes that the primary action

is a dissociation into two radicals by

a

rupture of a C-C bond, since this

is weaker than a C-H bond. In the range of temperatures between 700

and 1200°C. the chief dissociation product that has been recognized is the

methyl radical.

Frele methyl and ethyl have been obtained in the gaseous reactions be-

tween alkyl halides and sodium vapor (Polyani), and benzyl-as well as

methyl and ethyl-has been obtained by Paneth from the metal alkyls

by thermal dissociation. With arsenic, antimony, or bismuth, either

methyl or ethyl gives a number of different alkyl derivatives. The larger

radicals, propyl, butyl, etc. are too short in life to be detected by the

meana employed up to the present time.

Many photochemically sensitive molecules in gases give continuous ab-

sorption spectra; others give a few discontinuous bands on a continuous

background, while a few, such as benzene exhibit a discontinuous spectrum.

A

continuous spectrum indicates that the primary process is one of dis-

sociation into radicals, or into radicals and free atoms. The lapse of time

between absorption and dissociation is of the order of seconds for

continuous spectra to 10-lo in some predissociation cases. Free radicals

and atoms are the most important agencies in the propagation of chain

reactions, but excited molecules and atoms also play an important part.’*

In solution the probability of photochemical reactions resulting from

excited particles is increased, and that from free radicals decreased

so

far

as the primary stage is concerned. However, since the excited molecules

14 J

FRANCK

ND

E.

RABINOWITSCH,Free Radicals, a General Discussion.”

l ILIND

AND

GLOCKLER,

.

Am.

Chem.

SOC . ,

60 767 (1928); 61, 2811, 3655 (1929).

The

Faraday Society,

1933

p.

120.

8/11/2019 CME_01_01_052-064


64 WILLIAM D . HARKINS

are very rapidly deactivated by the molecules of the solvent, free radicals

and atoms are almost the only instigators of chain reactions.

It is evident to the student of these subjects that the organic chemistry

of electrical discharges, and the chemistry of organic radicals are

as

yet

only in the stage of a preliminary development, and that both of these

related fields are fertile for future discoveries by those who are well trained

in both physical and organic chemistry. While all possible methods of

experiment should be utilized, no established method gives more promise

than that of positive rays.

The methods of research utilized by organic chemists are very different

from those applied by physical chemists. One of the most urgent needs

of organic chemistry at the present time is tha t some of the workers in this

field be &st-class scientists in both fields.

It

may be said that the world

is almost entirely without individuals of this class. The universities should

be given unfavorable criticism for their failure to train at least a few

men, who as organic chemists, are also high-grade physical chemists and

physicists.

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