Long-range deuterium isotope effects in 13C NMR spectra of adamantane and 2-adamatanone

Journal of MolecularStructure, 267 (1992) 389-394 Elsevier Science Publishers B.V., Amsterdam

389

LONG-RANGE DEUTERIUM ISOTOPE EFFECTS IN 1% NMR SPECI’RA OF ADAMANTANE AND 2ADAMANTANONE

K. MLINARIhlAJERSKI,

V. VINKOVIC AND Z. ME16

Rudjer BoSkoviCInstitute,POB 1016,410Ol Zagreb, Croatia, Yugoslavia

P.G. GASSMAN AND L.J. CHYALL

Universityof Minnesota, Minneapolis, Minnesota 55455, USA

The availability of high field NMR instrumentation effects

(DIE)

knowledge mechanisms 2A

on carbon-13

chemical

of the dependence for transmittal

DIE on carbon-13

shifts (nA ) to receive

of DIE on chemical structure

molecules

in a few saturated

have been

to originate

explained

in molecular

from the

Long-range

conformations

and

effects of

systems. 3-5 DIE which are observed

by changes

1~

dependent

electron-releasing

that is other than through-bond.3l4

and the

Intrinsic

In contrast, 3~ effects appear to be orientation

or through a mechanism

isotope

study. Our

is still incomplete

shifts are well known and are believed

and their origin may be associated with either through-bond

have been observed

continued

of these effects are not fully understood.’

inductive effect of deuterium?

deuterium

has allowed deuterium

DIE

in flexible

which cause

secondary shifts over long distances.5 In this paper

we report long-range

spectra of adamantane

DIE through five bonds (5A ) in the r3C NMR

and 2-adamantanone.

We believe this to be the first example of a

5~ effect observed in a rigid saturated system. The

‘A

T2A ,3A ,4 A ,

shifts were determined

0022-2880/92/$05.00

and 5~ deuterium

for five monodeuterated

isotope effects in carbon-13 2-adamantanone

isotopomers

0 1992 Elsevier Science Publishers B.V. All rights reserved

chemical (1-S) and

390 for two dideuterated monodeuterated

Zadamantanone

adamantane

isotopomers

isotopomers

(6, 7), as well as for the two

availability of the dideuterated derivatives 6, 7, and 10 permitted additivity of the deuterium

1

(10). The

(8, 9) and for adamantane-2,242

us to evaluate

the

isotope effect on NMR shifts.

2

ff& f$$. D ‘D

Aydin

and

monodeuterated

Gunther

adamantanes

our measurements deuteriochloroform

nondeuterated

have

previously

reported

the

and nondeuterated

as the solvent, we were able to observe the as chemical

shifts of the carbon

Carbon-deuterium

the same solutions. At least three measurements The results of this study are listed in Table 1.

5~

resonances

relative to the chemical shifts of the corresponding compounds.

spectra

of

the

two

8 and 9,6 but failed to indicate any 5~ effect. By making

on a 3:l mixture of the deuterated

effects were measured compounds

10

7

6

adamantanes

effect. All isotope of the deuterated

carbon resonances

coupling constants were performed

in

were observed

of the using

for each isotopomer.

co.451

-22 tunres1 28 C(6)

LO.351

25 (C3)

to.01

27 (C5.7)

to.61

3A

t2J(13CD)1

~3)

(C5)

(~2)

(C4.9)

(C1.3)

t1.11

tunres1

(C3)

at 75.462 MHz. Values are given in ppb, digital resolution

0 (C2)

2.5

2 0.8 ppb.

5 (ca)

0 (C7)

0 (Cl)

(C’O)

Cl -25.1

+ 0.062 Hz. For 4A and 5A the coupling constants were zero or too small to permit resolution.

13C NMR spectra were recorded

2.5

2.5

(Ca)

0 (c7)

4 (C7) (Ca)

-20 5 (ca,lo)

4 (Cl)

0 (Cl)

0 (c6)

Cl.11

0 (Cl)

44

Il.251 13 (C’O)

(CIO)

(C9)

ktllreS1

61

tD.951

41 (C6)

32

(C9)

[unresl

(ca.9)

(C2)

kBW?Sl

-30

cunreS.1

II

El .‘I

32 (C4.10)

(C6)

0 C(2)

0 (C1,3)

tlKlWS1

43(c4,a,9,1D)

tli?l~~Sl

194 (C5.7)

0.2528

c19.41

a50

7 (Cl)

(c2.8.9)

(C3,5,7)

0 (C4,6,10)

co.91

32

co.51

128

0.2632

t2D.21

514

8

(~1.3)

4 (C6)

3 (C7)

0 (CS)

Cl.11

31 (ca.10)

~t8W~Sl

13 (C4.9)

to.51

loo

0.2515

t19.31

(C2)

9

s(i), of

440

(Hz)~ and the fractional s-character,

(C5)

wnres1

194

klnres1

170 (C3)

0.2593

34

(C2)

(C5.7)

0.lll~~Sl

97

0.2541

(~4)

c19.91

781

6

[I .I1 to.91

0%)

t19.51

424

5

(l-10).

27 (C9)

29 (C7)

LO.91

33

co.51

124 (C6)

co.41

119

0.2658

12 (C6)

10.71

-a

to.41

95

CO.61

a5

(CS)

C20.41

475

4

D (C4.10)

bDigitat resolution

%e

5A

4A

‘DO (C5)

122 (ca.9)

(C2)

CD.41

to.91

(C3)

a6

-41

(C2)

0.2606

0.2580

0.2750

(~4)

S(i)

389 c20.01

(~4)

tl9.81

389

c21.11

(Cl)

431

3

t’J(13CD)1

2

‘A

1

and 2-adamantanone

NMR isotope shifts (“A )a, the corresponding coupling constants

the 13CD-bond of deuterated adamantane

Deuterium-induced

Table 1

(C2)

(C1,3)

10 K6)

3 (C5.7)

to.651

46w4,a,9,10)

co.451

200

0.2515

119.31

aa3

10

392

Long-range

5~ effects were observed in the 1% NMR spectra of 2, 3, 6, 9 and

10.For both axial and equatorial

2-adamantanone-4dl

2 and 3, a 5~ effect of 2.5 ppb

was observed at C8. The additivity of these 5~ effects was demonstrated of 2-adamantanone-4,4d2 three compounds

(6) which showed an effect of 5 ppb. The 5A effect in these

were smaller in magnitude

10 (10 ppb). Experimentally,

than the related 5A effect in 9 (4 ppb) and

it is observed

that the presence

resulted in a decrease of the 5A isotope effect. Examination demonstrated

that

adamantane

the

introduction

skeleton

Presumably,

resulted

of an

of the

of the carbonyl

of molecular

sp2-hybridized

in a distortion

carbon structure

group

models clearly atom

into

the

of adamantane.

this structural distortion results in a decrease in the 5~ effect.

In general, it is observed 5A effects. The occurrence

across the adamantyl

E -carbon

4A DIE are similar or smaller in magnitude

electrons.

The observation

cage7 provides ample precedent

effect. In general

observation

that

of 5~ effects can be explained by a through-space

of the C-D dipole and the

isotope

by examination

is associated

-20 ppb was observed.

4~

effects range

interaction

of substituent

for this through-space

to

effects

deuterium

from O-5 ppb. The exception

to this

with C2 in compound 4 where an unusually large 4, effect of

Although

the carbonyl group is separated

from the deuterated

carbon in 4 by four bonds, the shift is at least four times as large as that observed for any other 4-bond

separation.

Again, examination and

n-orbital

Thus, a simple through-space

of the appropriate

of the carbonyl

“hyperconjugative”

interaction

group

molecular are

interaction

model indicated

aligned

in a manner

is unlikely that

for 4.

the C-D bond

which

permits

a

through the C3-C4 and Cl-C9 bonds.

The results listed in Table 1 illustrate the additivity of the 1~ -4~ DIE, as well as the geometrical

dependence

of the 3~

effects observed for compound compounds

and 4~ isotope effects. While examination

6 illustrates

the fairly rigorous additivity of the DIE for

2 and 3, it should be noted that the orientation

the carbonyl results in substantial

of the

of the deuterium

relative to

differences in the 3~ effects. To a first approximation,

393

the deuteriums membered

in 2 and 3 can be viewed as axial and equatorial

on a six-

ring, respectively.’

An additional dependence

feature

of our results is the demonstration

that an S-character

exists for the 1~ chemical shifts in the 1% NMR spectra for compounds

closely related structure, correlation methine

substituents

is observed

as was noted earlier, by Gunther for the

and methylene

correlations

are illustrated

1~

and co-workers.8

values and s-character

of

This useful

of the C-D hybrid for the

carbons of 1, 4, and 8 and of 2,3, 5 and 9, respectively.

These

in Figure 1.

‘A [ppbl

0.25

0.27

0.26

0.28

s (0

Figure 1. Correlation

between IA (1%) and fractional s-character9

of

8,

1 and 4

(A) and 9, 3, 2 and 5 (B).

In summary, we have illustrated that significant

5~ deuterium

isotope effects exist

in certain types of rigid molecules.

Acknowledgment.This work was supported by a grant from the Ministry of Science and Technology of the Republic of Croatia and by the National Science Foundation of the United States.

394

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