Dynamic NMR Technique Can Detect the Difference in Proton

CHEMISTRY

LETTERS,

Dynamic

pp.

1363-1366,

NMR Technique

1986. (C)

Can

1986

Detect

the

Difference

in

The Chemical

Proton

Affinities

9-[2-(Diethylamino)methyl-6-methylphenyl]fluorene Mikio

Department

of Chemistry,

+Department

School

of Chemistry,

The

proton

compound were of activation

CDCl3

was

16.4

the

the

same

the

the

difference

During

noticed

at

in

course

isomers that

compound

in

(1),

room

probable

the

ammonium

further

study

results

of

the

Toho

the

that

+

University,

Ota-ku,

University

sp

THE-d8

the

free

was

of

concluded

to

in

kcal/mol.

of

activation.

in CDCl3

interactions

are

and

in

the

be

responsible

ap

THE-d8, rotamer

to

_

investigation

rotamer while

on

the

difference

facts

and

the

of

the

phenomenon

the

trifluoroacetate

a broad

doublet

sp-rotamer

of

ion

investigation

of

showed the

The

candidate

143

the

the free rotamer

13.7

energy

kcal/mol

Tokyo

of Tokyo,

trifluoroacetates

in

13.4

NH-1π

the

of

in

basicities

of

9-[2-(dialkylamino)methyl-6-methylphenyl]fluorenes,2)

protons.

most

CDCl3

K,

and of

in

in

exhibited

14.1

1H NMR spectra ap

temperature,

the

it

of

of the

the

corresponding

of

OKI*

by the NMR method: whereas exchange process in the ap 298

presence

absence

the

rotational

at of

respectively.The

and

processes

sp rotamer

process

Michinori

Faculty of Science, The Bunkyo-ku, Tokyo 113

kcal/mol

contrast,

for

and

detected for the

of Japan

Rotamers1)

of Medicine,

exchange

title energy In

NAKAMURA

Society

imply the

that

and to

only

discuss

purpose the

the a

is

being

anion. the

salts for

there

phenomenon

trifluoroacetate

and

showed

we

a the

This of

this

implications

of

singlet rate proton finding paper

the

benzylic for

protons

the

process

taking

exchange allured is

diethyl

CH2N

to

therefrom.

place,

between us

present

to the

1364

Chemistry Treatment

with

of

a mixture

diethylamine

Chromatography of

of

the

dynamic The

by

the

ap

form

analysis

were was

constants Eyring

equation

results

are

by

taken

as

together shown

carried

the

half with

in

Table

Table

out

1.

of the

discussing

parameters, exchange.

with

the

amine the

Kinetic

the

which

chain

is

pure

compound

rich

use

of

JEOL

The which

constants,4)

to

produce

for

the

kinetic

in

ether.

FX-90Q The

rate

sp.

easily.

from

a

the

overwhelmingly

recrystallization

the

in

sp-form

was

DNMR3 program.3)

temperatures

Parameters in

probable

Compound

cause

it will be necessary There are two possible

free

called

the

is

The

instrument.

total

line

obtained

shape

rate

were

put

into

parameters.

the

The

1.

formed

mechanism

of

Proton

Exchange

1 Trifluoroacetates

for

to mention mechanisms

phenomena, Eqs. 1 and 2.5,6) Equation the ammonium ion and the trifluoroacetate of

which

tetrahydrofuran-dg.

real

Processes

Before

1,

the

by

or

use of

of

purified

chloroform-d

performed

were

be

of afforded

salts

could

was

either

rotamers

recrystallization

which

1986

9-(2-bromomethyl-6-methylphenyl)fluorene of

trifluoroacetate

NMR measurement

solvents

rotameric

a mixture

followed

Equilibration favor

of

afforded

Letters,

the

difference

in

on the mechanisms that can explain

1

is the anion,

in

a minute

amount

the

proton

exchange.

of the

mere exchange whereas Eq. in

the

kinetic

2

the proton observed

of proton represents

system.

The

NMR

between the second

role

can

(1)

(2)

The

line

amount

of

ap-1.

The

As like

to

the rules because,

exchange effect ascribe

by of it

NMR

spectra

of

out

the

if

virtue

it

of

anion,

the

0.12 added

should

did

equivalent

possibility were

of

not

change to

case, the

in

of bond

in

2

as

the

up the

addition

concentration

excess

hydrogen result

Eq. the

to

added salt

mechanism

of

the

equivalent,

between

the of

of lower

free

the

the the

amine. we

acid

of

0.12

should

0.12

weakening

the

dissolved

acid

of

the

until

the

trifluoroacetic

acid

formation which

40 C

diminishing

trifluoroacetic to

at

reached

effect

proton,

the

trifluoroacetate

of

definitely

of

to

the

acid

absence

of

rates

of

trifluoroacetic

equivalent exchange

shape

and proton-

should the

be

Chemistry Letters, 1986 accepting

ability

proton

CDCl3 gives salt

the

a very and

presence

form,

of

to

the

enthalpy

and

obtained

by the

obtained

will

by careful enthalpies

The

enthalpy

of

is

larger

little

too

because

large

even

kcal/mol9)

enthalpy

OH-'l hydrogen

the

largest.10)

It

difference

contains

the

to

sp due In

close

indicate

do The

exchange

the

not

form

process

ion

in

ion

pairs

the

increase

in

the

of

either

activation ap

chloroform.11) salts the

in bond

to

freedom

ap-1

salt

motion

sp-1

form

is

important it

whereas

exchange of

form,

the

of

three

to

equivalent

in

the

to

form

is

applied

activation atoms.

the

ground

oxygen state

a partial to can

decrease

the be

We should

in the atoms

but

in

with

the

bond

with

case

examined

expected like

to

freedom

8 kcal/mol

very

because

proton

in

solvent

an

oxygen

results atom

Thus

in only

here, the that

of

motion can

the

a small

is

we solvents

positive

others

for

are

ammonium This

molecules.

state on

to

similar

The

form.

is

positive,12)

it

transition

the

suggest

which

at

relative

ion is

the

all

negative.

with

chloride

attributed

However,

in

to a similar

proton exchange process between an ammonium ion and sulfonate anions, the of activation becomes small negative or close to zero.13) This has been attributed

bond:

2 kcal/mol

NH group.

interesting:

large

a

ca.

of

an

ap

in

OH-0 hydrogen

give

ap

below.

ap

of

chloroform-d. bears

thus

may be

the

value

the

the

in

stabilized

in

also

very

and in

shape

salt

This

the

even

the

ap-1

formation is

line

we may have

It-system,

bond

in chloroform-d,

be

form

by THE which

proton

of

of

sp-1

with

are

ap

data

and

the

the

than of

the

case,

enthalpy

of

sp

that

described

bond

the

the

reservations.

experimental

the

solvation

for

known

the

when

in

be less

by

form

activation the

that

of

has

to

into

true

8 kcal/mol.

enthalpy

that

the

hydrogen

are

the

NH-u hydrogen

of the

should

have

both

by

basicity

and/or

that

the in

entropies

to

activation

also

significant

NH-It hydrogen

weak

of

activation

process

bonding

the

be

of

salt

the

hydrogen

NH-Ir interaction

entropies

The

to that

to

that

to

error

contrary,

the

1 should

the

molecules

this

some

to

activation

energy

is

in

with

entropies

wholly

NH-it bond

on are

and

sp-1

possible

some

relative

conclude

is

in Table

exchange

known

effects

which strongly

the

is

solvation

THE-d8,

important

of

bond

simple

in

in

of

free

energies it

salt

absent

solvent the

reproducible

activation

the

considers

one

are

the

if

free

rather

of

OH-0

formation

the

results,

attribute

of

the

relative

energy

of

of

may be attributed is

free

we divide

ap-1

process

which

the

mechanism the

This

controversial,

for that

strongest

and,

of

than

if

are

of

seen

the

form,2)

analysis

enthalpies

for

since

the

that

contributions

is

entropies

the

ap

division

shapes

activation

to

the

has

shape

line

differences on

the

insight, the

line

and

large

which

the

by Eq. 1. it is apparent

tetrahydrofuran.

in

better

that

activation

in

NMR technique

total

discussion

which

therefore

However,

Although

dynamic Since

chloroform-d

of

salt

interaction

much

entropy.

the

deserve

energy

ap-1

activation

give

complex.7'8)

However,

free

the

NH-'t

of

it

will

We conclude

approximation.

entropy

to discuss

to

first

involved,

10

anion.

large

even of

the

contains

is

the

exchange we are observing is shown one looks at the data in Table 1,

If sp-1

1365

of

have

the

anion:

interactions the

oxygens

ammonium

one

of

ion.

If

negative

or

carboxylate

anion

the

of

entropy

near has

activation

the

anion

with

the

cation

be

bound

must

this zero

two

entropy bears

explanation entropy

of

equivalent

oxygen

of

cal

ca.-10

1366

Chemistry Letters, 1986

mol-1 the

K-1

is

abnormal.

the

for

entropy

of

activation

be

caused

This

formation of

normal

positive

the

of ap

must

the

form

the

bond is

in

process by

the

of

the

proton

for

the

exchange

the

ground

restricted

but

presence state,

the

proton exchange, because the In summary, we were able to

exchange in

of

the

the

examined

the

ap-1 motion

increases

in

the

bond first

is partially time that

freedom

of

Then

in CDCl3

NH-7r hydrogen

freedom

NH-7 hydrogen show for the

here.

salt

bond: in

the

by state

broken. the proton

exchange

rotamers.

governed

rates

and

will

contribute

solvents

as

This of

are

interactions. to

well

work

Education,

as

the

the

was

intramolecular

method

knowledge

basicity

supported

Science

by

The

of

of

applied

basicity

of

rotational

by a Grant

and

interactions

may be

Culture,

as

to wide

amines

in

chain

transition

the dynamic NMR technique in an ammonium carboxylate could be different to a large extent for respective

The

the

side

process was detectecd by the rates of the exchange solute-solvent

is

well

and

as

variety

the

of

various

of

amines

aprotic

isomers.

in Aid

to which

for

our

Scientific

thanks

Research

are

of

Ministry

due.

References 1)

Part K.

XVII

Soc. 2)

of

the

Yonemoto,

series

F.

Jpn.,

58,

M.

Nakamura

3)

G.

Binsch,

4)

E.

Grunwald,

5)

F.

6)

C.

L.

7)

G.

Binsch

8)

M. Oki,

"Reactivities

Kakizaki, 3346

and

6ki,

Chem.

Stable

N.

Lett.,

Stereochem.,

C.

of

Yamamoto,

Rotamers":

Nakamura,

and

for M.

Part

bki,

XVI,

Bull.

see

Chem.

(1985),

M.

Top.

G.

F.

3,

1985,

97

255.

(1968).

Jumper,

and

S.

Meiboom,

Singh,

and

F.

L.

J.

Am.

Chem.

Soc.,

84,

4664

(1962). M. Menger,

T.

D.

Bayer,

J.

Am.

Chem.

Soc.,

98,

5011

(1976). Perrin

and and

G.

C.

M. Oki, M. Oki

11)

It

Pimentel

the

H.

still

H.

in

M. Ohira, Soc. and

the

are

Jpn.,

Y. 57,

M. Ohira,

104,.2325

Int.

Ed.

Chap.

(1982).

Engl.,

NMR Spectroscopy

to

19,

41

Organic

(1980).

Chemistry,"

VCH

1.

"The

Urushibara, 33, the

Hydrogen

Bull. 717

Bond,"

Freeman,

San

effects

significant

be

a

in the

exchange

2224

(1984).

Bull.

Chem.

the

conformation

to

Morita,

Soc.

Jpn.,

31,

770

(1958):

57,

(Received

3117

group

which

expected

which

Kihara,

N-ethyl in

are

molecular

H.

Jpn.,

the

effects

conformation

according T.

Soc.

between

steric

stable

Yoshioka,

Chem.

(1960).

steric

Although can

proton

Chem.,

McCllelan,

ibid.,

place. there

Soc.,

(1985),

Y.

that

nucleus take

Dynamic

Chem.

7.

Iwamura,

M. Oki,

M. Oki

L.

and

possible

crowded

Chem.

A. Chap.

Iwamura,

conformations,

13)

of

Am.

Beach

and

fluorene

exchanges

12)

Angew.

(1960),

and

is

Kessler,

Deerfield

Francisco 10)

J.

"Applications

Publishers, 9)

H.

W. Wang,

is

the in

not

and proton

many

sterically

models. and

N.

Nakamura,

(1984).

June

6,

1986)

Bull.