title the effect of pressure on the keto-enol...

Title The effect of pressure on the keto-enol equilibria of acetoneand cyclohexanone

Author(s) Osugi, Jiro; Mizukami, Tetuo; Tachibana, Tadafumi

Citation The Review of Physical Chemistry of Japan (1966), 36(1): 8-19

Issue Date 1966-10-30

URL http://hdl.handle.net/2433/46874

Right

Type Departmental Bulletin Paper

Textversion publisher

Kyoto University

The Review of Physical Chemistry of Japan Vol. 36 No. 1 (1966)

THE REVIEW OP PHYSICAL CHE]IISTRY OP JAPAF, VOL. 36, NO. 1, 1966

THE EFFECT OF PRESSURE ON THE KETO-ENOL EQUILIBRIA OF ACETONE

AND CYCLOHEXANONE

BY ]IRO ~$l:GI, TETUD '-1IIZl.'a'.ASti A\n TADAFI:3dI TAC}iIBANA

The etTect of pressure an the ke[o-enol equilihria of acetone and cyclohexanoae in the solvents of carbon disulfide, toluene and n-hexane has been studied by the measurement of the infrared spectra a[ high pressure: Comparing the molal volume of the keto form with that of the enol form, it is expected that the enol from is favorable with increasing pressure. In this study, this expectation has been con-firmed. That is, the keto-eaol equilibria of acetone and cyclohexanoae shit[ [o [he enol form with increasing pressure.

However, the absolute r•alue of the enol concentration is yet small. For ex-ample, the value of the ke[o-enol equilibrium constant, K=(enol)/(ketn), for ace-tone in n-hexane is 1.6 x 10'2 al a pressure of SOOO kg/cm2, and that for cyclohex-anoae in x-hexane is 3.6 x 10-2 at the same pressure.

.Acetone and cyclohexanoae are the monake[ones of the aliphatic and the cyclic structure, respectively, and the pressure effect on the keto-enol equilibria is larger for [he former than for the lacer. This difference may he due to the structural diRerences between acetone and cyclohexanoae.

As for the solvent effect on the keto-enol equilibria, the concentration of the eaol form of acetone and cyclohexanoae in the solvent of n-hexane are much higher, and in general the enol form increases in mhexane. This tendency is also confirmed is this experiment. The concentration of the eao] form of acetone in carbon disul-fide and is toluene are much [he same, but for q'clohexanoae the concentration of the enol form is carbon disulfide is higher than in toluene.

Introduction

Since K. Jieyerll had determined the concentrations of the enol forms at equilibria for some

ketones by the so-called K. ~Ieyer Method which is based upon the fact that the enol form absorbs

bromine rapidly, the studies on the keto-enol equilibria were carried out for many substances. The other

titration method using iodine monoch!oride was also reported'->.

The molecular refractioaal, the ultraviolet spectrum+> and the infrared spectrums) were also used

as [he means of studying the keto-enol equilibria in comparison with the titration method.

(Received Augutl S, 7966) t) K. ilIeyer, Ber.. 4d, 27Z5 (l9t I), 45. 2843 (1912) 2) A. Gero, J. Org. Chem., t9, 469 (1954) 3) K. con Auwers, Bn., 72 A, tll (t939) 4) A. S. N. Murthy, A. Balasubramaniaa and C. V. R. Rao, Can. !. Chem., 40, 2167 (1962)

0. S. Hammond, N. G. Borduin and G. A, Giuter, J. Am. Chem. Sot., 8i. 4682 (1959) 5) R. \fecke and E. Funck, 7.eil. Blekhockemie, 1124 (1956)

L. J~ Bellamy and L. Beecher. J. C2rem. Sac., 4487 (1954)

The Review of Physical Chemistry of Japan Vol. 36 No. 1 (1966)i

The E6ect of Pressure on the Iieto-Enol Equilibria of Acetone and Cyclohecanone 9

In the studies on the keto-enol equilibria by the infrared spectrum, the~C=O stretching region at

about 1100cm-~ and the ~C=CG stretching region at about 1600tm-r were generally useds>. Especially,

the keto-enol equilibrium of etbylacetoacetate was im~es[igated in detail by using [hose regions.

As for the e6ett of pressure on the keto-enol equilibria, Kabachnik eE aPl. and Le koblee~ studied

it for ethylacetoacetate. Hox•ecer. in these studies the concentration of the enol farm was determined

by the titration method after releasing pressure.

In general, the substances used as samples of the studies on the keto-enol equilibria were ethylaceto-

acetate or a-diketones. Then, little attention has been paid to the keto-enol equilibria os monoketones.

This paper reports the results obtained from the studies of the pressure effect on the keto-enol equi-

libria of acetone and cydohezanone by the measurement of the infrared spectra at high pressure.

Experimehtals

Acetone, cydohexanone and benzaldehyde. and carbon disulfide, toluene and n -hexane, commercially

offered as guaranteed reagents, treated with the ordinary purification method, were used as the samples,

and the solvents, respectively. These solvents were chosen From the view of the following criteria.

1. No absorption band in the experimental range of wave numbers.

2. too solidification at the experimental pressure.

3. i~o reactivity with the carbonyl group.

4. Fo corrosive action to the optical vessel.

Then, the polar solvents, such as alcohols, chloroform, methylene chloride, etc., were not used in this

study.

The apparatus used is [he same as reported in the previous paper9~. When this optical vessel is used

for the measurement of the infrared spectrum, the response of the spectrometer is very slow. Then, after

getting balanced posivons, the dots of the recorder pen were obtained at the in[en•al of 10,-20 cm''. The solution of 1 mole,llwas always used in this experiment, for this concentration was suitable for

the measurement of. the absorption spectra at high pressure, owing to the path length of the optical

vessel.

The measurement was performed at the pressures of 1, 2000, 4000, 6000 and 8000 kg/cmZ for each

solution.

On the other hand, the apparent extinction coefficients of each solution at 3400 em'' aad the relation

behveen the concentration of OA group and the apparent extinction were obtained by using an ordinary

optical cell with potassium chloride windows. The experiments were carried out in the room conditioned

at 20-C, though the temperature of the optical ce<_sel for high pressure measurement was not regulated

by any special method.

6) R. J. W. Le Ffvre aad H. Welsh, J. Chem. 5oc., 2230 (1919) I)lf. L Kabathnik, S. E. Pal-ushl-i na, and \. V. KislyaAova, Doklady. Akad.:\'uak. L'. R. S. S., 96, 1169

(1914) 8) R'. J. Le Soble. !. Am. Chem. Soc., g2. 5253 (1960)

9) J. Osugi and 1'. Kitamuca, This laun~uL 35. 25 (1961).

i i


10 J. Osugi, T. 1lizukami and T. Tachibana

Results and Considerations

Absorption band of the enol OH stretching vibration

Up to the present time, the ~C=O stretching region and the >C=C< stretching region were used

in the studies on the keto-enol equilibria by the infrared spectrumst. Howeveq these regions are not

used in this study, since the sapphire window has no [ransmittance in these regions.

It was reported that the enol OH stretching vibrations of ethylacetoacetate and S-diketone such as

acetylacetone were found in 2500~2800cm-tto). This fazt was explained from the view that [he enol

OH group in these substances would form the Conjugate chelation with the strong intramoletulaz hydro-

gen bond, because of the shift of the OH svetching vibration to the lower wave number. However, Calvert e! oltt>. reported that the OH absorption band of the enol acetone in the photo-

lysis of 2-pentanone vapor was found at 3629crn ~ in vapor phase. Accordingly, since methanol has the

absorption band of OH a[ 3682cm-~ in vapor phase and phenol has an analogous structure to the enol

v

N C n

F

HO

70

Fis. I

fi0

50

.m

an

tl0

m

~0

c 50 a c

F

,o

•\ ,

,

11

G'

~>o , ,~ 3700 ;16W ~ 3700 3300 3'!00 3i00 3600 3600 3700 3:100 3:00

Wave number (cm-') Nave number (cm'') Spectra of acetone and methanol in acetone. Fig. 2 Spectra of cyclohezanone and phenol in cy

(0.05 mole/f) clohexanone (0.05 mole//) Full line: acetone Full line: cyclohexanone

Broken line: methanol in acetone Broken line: phenol in cyclohexanone

10) R. S. Rasmussen, D. D. Tunnicliff and R. R. Brattain, 7. Am. Chem. Sot., 71, 1068 (]949) S. Bratoz, D. Hadzi and G. Rossmy, Trans. Faraday Sac.. 52, 464 (1956)

! t) G. R. Mchfillan, J. G. Culvert and J. \. Pitts, 1. Am. Chem. Soc., 86. 3602 (1964)

The ESect of

911

xn

i0

v u

C m

.~ m C

m

F

r~

Pressure on [he

The Review of Physical Chemistry of Japan Vol.

Keto-Enol Eq uilihria of Acetone and Cyclahexanone

-,

~- ~,

ly

~ ~ i i ~

36 No. 1 (1966)

36011

Fig.

100

90

U_

~E

e .o

m F

so

so

Fig. 4

form of cyclohezanone, r

shown in Figs. 1 and 2, r

The absorption banr;

Lion. However. as shown

3500 3400

3 Spectra of

Full line

Broken 1

39]0 32C0 3600 3500 3)00 3300

Wage number (cm't) acetone in n-hesaae at 2000 kg/cmZ

after Z hours ine: after 20 hours

3200

~ ~• _~ ~ ~

~ ! 1 /

I /

1 ~

I I

1 ~

1 ~

I ~ 1~

I~

IJ/

1 I I 1 I

3600 3500 3100 3300 3_'~W 3600 3500 3400 3300 3200

Wave number (cm-t) ig. 4 Spectra of cydoheaanone in carbon disulfide at 8000 kg/cmr

Full line: atter 2 hours Broken line: after 20 hours

ne, methanol in acetone and pbenolin tyclohezanone have [he infrared spectra as

2, respectively.

band at 3400cm'' in these spectra is the overtone band of ~C=O stretching vibra•

sown in Figs. t and 2, it is assumed that the enol OH absorption bands of acetone


t2

sg

ro

.o

k V ~ F

ii ~ 9

F

90

1g

rkg/®'

~r

J. Osugi, T. Misukami and T. Tachibana

msokghm' 40gaYg/rm~

1 I 1

6oookg;vm~ eaWkrkm'

YAa 1500 31W ]]pp yql ~ J9C0 3.TD YiU 1+G1 Jim IrII/:WX1 ]Yq JIIXI ]arl ]Gy ;l4Nl y9ry1 l]b

{Nave number (cm-II Fig. 5 Change or [he apparent transmiuance of the spectra of acetone in toluene by pressure

(1 mole/1)

and cyclohexanone overlap with [he overtone band, respectively. Then, the effect of pressure on the ab-

sorption band at 3400cm-t was studied.

Time required to reach at equilibrium after wmpression

The time required to reach at equilibrium after compression is examined. As shown in Figs. 3 and

4, there is no difference between the spectrum after 2 hours at the definite pressure and that after 20

hours, and the system is allowed to reach at equilibrium in 2 hours, so that measurements of the spectra

were carried out after 2 hours' pressing.

Effect of Pressure on the keto-eaol equilibrium

The apparent absorptions at 340D tm'~, of 1 mole/1 solutions of acetone, cyclohexanone and benzal-

dehyde in the solvents of carbon disulfide, toluene and n-hexane were measured a[ the pressures of 1,

2000, 4000, 6000 and 8000 kgfcmt. The result obtaiced for acetone in toluene is shown in Fig. 5 as an

example.

Acetone and cyclohexanone may be in the keto-enol equilibrium as shown in equations (1) and (2),

respectively.

CH3 C-CH]~CH1-C=CH] ~ ~ (1) O OH

H, HZ HZ H

HZC<C-C ,C=O~HrC<C-C~C--0H (2 ) H, HZ/ Hi Hz

The molal volume of acetone is i ~.3 cm' and that of ally) alcohol, CH]=CH-CHsOH, which is the


The EBect of Pressure on the Keto-Enol Equilihria of Acetone and Cdohexanone I3

alcohol type isomer of acetone, is 68.0 cma. The latter is smaller than the former. On the other hand,

the parachors~> of the keto forms and the enol forms of acetone and cydohexanOne are calculated. The

parachor is represented by equation (3),

r

P=hp d (3 ) where 37 is the molecular weight, Y is the surface tension, D is [he density of liquid phase and d is that

of gas phase. In equation (3), in the keto form and the eno] form. N1 is the same, d being negligible by

comparing with D and assuming to be 7.~-]'eT- Then, equation (4) is deduced. In equation (4) suffixes

e and k represent [he [he enol form and the ke[o form, respectively.

The density of the enol form is calculated by equation (4). Then, [be molal volume of the eool

form is estimated. The results are shown in Table 1. That is, the mOlal volumes of the enol forms of

acetone and tyclohexanone are smaller than those of the keto forms, respectively. The molal volume of

the enol form of acetone calculated by the parachor is essentially equal to [hat of ally) alcohol.

9ccordingly, it is expected that the keto-enol equilibrium shifts to the enol side with incre~ing

pressure. As shown in Fig. 5, the apparent absorptions increase with pressure. It is considered that the

increases of the apparent absorptions of acetone and tyclohexanone are due to the shift of the keto-enol

equilihria to the enol side.

However, the tendency that the apparent absorption increases Leith pressure was also found in the

previous paper93. In order [o study [he influence of pressure on the overtone band of ,C=O stretching

vibration, the apparent absorptions at 3400cm-[ of benzaldehyde, which has not the enol form the view

point of the molecular structure, were measured in [he solvents under high prevure.

H H C-C HC~ ~C-C-H bcnzaldehyde

C=C ~I H H O

On the other hand, the apparent extinction coefficients of these samples at 3400cm-t were obtained

ie each soh•ent. The results are shown in Table 2.

Tablet Calculated molal volume at 20'C

Type Parachor Density b'lolal volume (g/cm~) (cml/mole)

acetone

tyclohexanone

allyl alcohol

ke[a

enol

keta

eml

Ic1.4

148.9

2i0.8

138.3

0.792

0.858

0.947

0.991

0.854

i 3.3

67.1

103.6

98.3

68.0

12) 0. R., Quayle Ckern. Rev., S3, 439 (1953)

i14

Tahle 2

The Review of Physical Chemistry of Japan Vol. 36 No.

J. Osugi, T. \Iizukami and T. Tachibana

Apparent extinction cce~cien[ aL 3400cm t (ea; I/mole.cm)

1 (1966)

Soh•ent Aatone cyclohexanone Benzaldehyde

carbon disulfide

toluene

n-hexane

i.51

6.85

7.91

7.69

7.64

T.63

i.81

9.21

1 L24

Table 3 Ea

SolventPressure (kg/cm~

1 2000 4000 6000 8000

acetone

carbon disulfide

toluene

n-hesnne

i:il

6.83

7.91

lLi

12.4

13,3

I S.D

19.3

19.6

19.9

1i.fi

26.7

23.4

31.5

33.2

cyclohexanone

tarbon disulfide

toluene

n-hexane

i.69

i.fi4

7.63

12.6

Y3.9

12.6

t8.1

10.4

18.9

20.6

25.4

24.5

25.9

32.0

30.8

benzaldehyde

carbon disulfide

toluene

n-hexane

i.81

9.21

11.24

10.4

14.2

Id.3

12.1

19.1

20.7

14.7

23.0

23.fi

18.1

29.0

28.0

Supposing that Beer's law (5) holds, the change of the appnrent extinc[io¢ with pressure is calcu-

lated by equation (6) from the experimental results. In equation (6), sa is the apparent extinction coeffi-

cient, T„ is the transmittance at pressure of P, and T1 is that of 1 kg/cros. E, is shown in Table 3.

std=ln ~° (5 ) log Tp Eo=t"Io TT (6 ) g t

The relativevolumes of the samples and the solvents are shown in 'I'ahle 4. The values for acetone,

carbon disulfide and n-hexane are the data of P. N. Bridgmantal, but those for toluene, cyclohexanone

Table 4 Relative eolume at 20~C (V,/Vt)

pressure (kg/<m~

2000 4000 fi000 8000

acetone

cyclohexanone

benzaldehyde

carbon disulfide

toluene

n-hexane

1.000

1.000

1.000

1.000

l.eoo

1.000

0.667

0.901

0.915

0.896

0.896

0.864

0.786

0.846

0.867

0.843

0.844

0.812

O.i86

(0.818)

(0.835) 0.811 0.800

O.i i6

0.768

(0.806)

(0.820) 0.784

0.772 0.753

t3) P. N. Bridgman, "The Physics of Aigb Pressure;' p. 128 (1958)


The E6ec[ of Pressure on the Re[o-Enol Equil ibria of Acetone and Cyclohexanone t5 i

and 6enzaldehyde were measured in our laboratory. Pure cyclohesanone andbenzaldehyde solidify at pres-

sures of 4400 and 4i00kg/cmr, respectively. However, it is found that they do not solidify in solutions

a[ a pressure of 8000 kg/cm2, bul they may 6e in super compressing. Then, the relative volumes of these

samples a[ pressures of 6000 and 5000 kg/cmz were obtained by the extrapolations of volume-pressure

cun~es below the freezing points.

E'a is the appazent extinction obtained by equation (i).

E'o is the value which is corrected for the change of the concentration due to compression. Plotting E'a

against pressure, the linear relations n•ere obtained as shown in Figs. 6--8. In Figs. 6^-8, the apparent

extinction of 6enzaldehyde also increases with pressure. But, as benzaldehyde does not change to the

enol form from the riew point of its molecular structure as described above, it is concluded that the increase

of the apparent extinction of 6enzaldehyde is brought by pressure itself, and not 6y the enol form.

It is assumed that the coefficient of the change of the apparent extinction of each sample by pressure

itself would be equal in the same solvent. Accordingly, the increase of the apparent estinclion of the

OH group due to the shift of the keto-enol equilibrium to the enol side with increasing pressure is re-

presented by the difference behceen the increment cf the apparent estinclion of acetone or cyclohesanone by pressure and the increment which multiplied [te apparent extintion of acetone or cyclohesanone at

ordinary pressure by the pressure coefficient of the 6enzaldehyde in the same =_olvent.

This relation is represented by equation (8), where Eao is [he apparent extinction of the OH group,

E',,, and E'„r are the E', for acetone,

3

15

m

s

t

0 X100 ~Pll 6N0 flMq

Pressure Ikg/cm= ) . 7 Change of [he apparent extinction at 3400

cm'1 by pressure ~ : ate[one in toluene

x :cpclohexanone in toluene benzaldehyde in toluene

zs

,~

L{; IS

le

s

Fig Fig. 6

o :row sow ruo soon

Prmure (kg/cm' 1

Change of the apparent extinction at 3400 tm r by pressure

0 :acetone is carbon disulfide x : cyclohexanone in tarbon disulfide

~ : benzaldehpde in carbon disulfide

I

I II

I

i

Ifi

w

?s

15

10

5

The Review of Physical Chemistry of Japan Vol. 36 No. 1

]. Osugi, T. dlizukami aad T. Tactibaaa

O

x~

0

u

m

~e

m

o Z90a 1000 soon Ban

Fig. g Change of the appare cm-r by pressure

~ :acetone in n-be x : cytlohexanone

O ; benzaldehyde i

or cytlohexanone at pressur

dehyde. For example, in th

extinction shown by arrow 1

pressure.

However. E,~ involved

Accordingly. the correction

The value of E'ce is the app

enol equilibrium to the enol

On the other hand, usi

cyclobexanone, the apparen

in Fig. 11. That is, the app

phenol in cydohexanore. A

extinctions and the concentr

the enol OH group. Then, t

is shown in Tabte 5 as the

The ratio of the increas

than for cytlohexanone. Th

i.

~-

o moo wa sooo eooo nt extinction at 3400

Pressure (kg/cm= ) xane Fig. 9 Correction for [be change of the apparent in n-hezane utinction by pressure o n-hexane Full line : acetone in carbon disulfide

Broken line: correction lint

es of P and 1 kg/cmz, respectively, and E'~e, and E',,, aze tho=_e of benzal-

e case of acetone-carbon disulfide system (Fig. 9), the value of the apparent

ine is the apparent extinction of the enol OH group which is increased by

the change of the apparent extinction by preuure iuelf as mentioned ahove.

is carried out by equation (9). The relation is shown in Fig. 10.

E'oa=E~~i a ~s~ (9 ) arent extinction of the OH group which is increased by the shift of the keto-

side in equations (1) and (2) by pressure.

ag the low concentration solutions of methanol in acetone and phenol in

t extinction of the OH group is L•etones was measured. The result is shown

arent extinction of methanol in acetone is in good agreement with that of

ccordingly, it is not unreasonable that this relation between the apparent

a[ions of these substances is used for the estimation of the concentration of

be concentration of the enol form teas determined by this re]atioa. The result

keto-enol equilibrium constant.

e of the keto-enol equilibrium constant with pressure is larger for acetone

e=_e increases with pressure are shown in Figs. 12 and l3.

(1966)


The Eaect of Pressure on the Reto•Enol Equilibria of Acetone and Cytlobezanone 17

s

a

w

%'

~' ~- .

_'OCO 40IX1 NYU Well

Correction for the change of the apparent

extinction by pressure

Ful I line : Eao

Brocken line: E',o

6

i

3

Fig. 10

Y

Fig.

e 05 Lo 1.5 2A

(~ 10-'~mole/0

Concentration of OH

1 t Relation between the concentration and the apparent extinction of OH group

x :methanol in acetone

~: phenol in cyclohexanone

Tahle 5 Equilibrium constant at 20'C

Pressure (kg/cm~Solvent

7 2000 4000 6000 8000

Kax t03

carbon disulfide

toluent

n-hexane

0.31

0.40

0.61

1.36

2.46

4.3i

a.47

4.57

8.42

6.59

6.70

12.71

8x7

S.7s

16.50

K, x IN

carbon disulfide

toluene

n-hexane

2.05

z.o4

2.09

2.36

2.31

2.44

2.64

2.53

1.83

1.95

2.80

3:12

3.x4

3.05

3.60

K~-(cool)/(ketoJ(acetone) (cyclohexanone)

dV obtained by equation (10) is shown in Table 6. On the calve 81nXl _ QV (10) ~oP /T RT

of dV, there is a large difference between acetone and cyclohexanone. It is concluded that this difference

is owing to the aliphatic structure of acetone and the cyclic structure of cyclobexanone. In the molal

volumes of the keto form and the cool form of these substances calculated by the parachors, the differences

between the keto form and the cool form are mucb the same for these substances. However, for the cool


I8 ]. Osugi, T. Afizukami and T. Tachibana

IS

m

s

n ~aa sooo soap soda

Pressure (kg/rm=)

l2 EHect of pressure on the keto-cool equilibrium constant of acetone in solvent

~ : n-hexane Q :carbon disulfide

x :toluene

Tah1e 6

]5

vn

!5

°y

Fig,

n row 1ma soap paw

Pressure (k8/cmr 7

Fig. l3 EHect of pressure on the keto-cool equilibrium constant of cydohexanone in sol-

vent

~ : n-hexane O :carbon disulfide

x :toluene

SolventPressure (kg/cmr)

7 2000 4000 6000 8000

azetone

carbon disulfide

toluene

n-hexane

-2:.4

-2.6

-231

- los

-11.2

-11 .7

-3.3

- 3.3

-3 .8

-3A

-3.1

-3 .6

- 2.4

-2.4

-1 .6

cydohexanone

tarbon disulfide

toluene

n-hexane

- 2.1

-1 .8

-2.3

-LS

-1 .3

- 1.7

-1.3

- 1.1

- 1.5

-L2

-1.0

-1 .3

- L0

-0.9

_t1

form of cydohexanone, the ~C=C~ double bond should be produced in the six membered ring. Owing

to this double bond the stric[ion is made in [he sis memhered ring. For this reason it is supposed that

the shift to the cool form is retarded. On acetone, as there is no steric hindrance, the ratio of the enoli-

zation is higher comparing to cydohexanone. From the view that acetone is in associated state. the value

of dY {or acetone is understandable.

As for the solvent effect, the enolization of acetone or cydohexanone is highest in n-hexane. It was

previously reported that the concentration of the coot form increased in n-hexane. This tendency was


The Effect of Pressure on the Aelo-Enal Equilihria of Acetone and Cydohexanone

also Confirm ed in this study. The enolization of acetone in carbon disulfide and in toluene are much

same, but that of cy-clohexanone in carbon disulfide is larger than in toluene. This may be asvibed

the effect of the steric factor on the keto-enol equilibrium. -

The authors are grateful to the

Acknowledgment

Furashiki Rayon Co., L[d. Ior their aids.

Laborolory of PJrysial Chemistry

Deparhnent of Chemishy

Focally of Science

Kyoto University

Kyoto. Jaymt

19

the

to

i

14) K, ilIeyer and P. Rappetmeier, Ber., qq, 2718 (1911) R. J. W. Le F2vre and H. R'elsh, !. Clrern. Sac., 1909 (1949)

title the effect of pressure on the keto-enol...

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