Molecular association of pentanols in n-heptane III : Temperature and concentration dependence of proton NMR chemical shift of hydroxyl group.

MOLECULAR

ASSOCIATION

TEMPRRATURR

AND

CHEMICAL

MANIT

OF

PRNTANOLS

CONC EWI'RATION

SHIFT

OFEFyDROXn

RAPPONl

5 October

DEPENDENCE

OF

III-:

PROTON

NMR

Mm JOHNS

Lakehead

Department of Chemistry, Ontario, CanadaP7B 5El (Received

n-HEPTANE

GROUP-

CBARD

andRI

IN

University,

Thunder

Bay,

1988)

ABSTRACT

'H NMR -OH

the

group

n-heptane = 0,003 The

has

for

over to

chemical similar

(AH)

of for

approximately almost

reasons

for

discussion Kerr and

related

o whom

same.

as

13

and C NMR

large

difference

The as

different.

viscosity relaxation

and

magnitude those

for

in AH

in ccqparison

other

with

the

313

K,

of

the

OH

follows

the

changes

The

values

for

in of

3-pentanol

are

t-petntanol

pentanols,

are

known of

F

the

of

of /\H

values

measurements and

fit

dependence

2-pentanol

to

limitations

However,

are

in

223

to

of

fraction,

concentration

pentanols,

1-pentanol,

Is made

effect the

the

all

and

of

used

and

the

general,

(mole

span

been

shift

pentanols

range

validity

H-bonding

the

twice

has

chemical

of

temperature

temperature

for

the

mixtures

model

In

on

trends

obtained

is

the

The

explored,

study

concentration

results,

shift

enthalpy AH

a wide in

to

binary

association

experimental are

applied

the

1.000)

linear

model

been

The

offered.

The

information the

Klrkw&

same

g-factor

from

system of

alcohols.

ccrrcapondence

oie7-7322/89~&.6o

should

he

addressed.

.U3 1969Elaevier!3cien~Publif8benB.V.~ ‘:

..

.’ . .

166 INTRODUCTION

Alcohols important they

when

roles

can

the

stereochemistry

of

the

is

better

to

knowledge

on

improving

our

products

[2,31

to

the

led

called

Therefore,

in

roles,

on

formation

of

order

to

need

to

enhance

in

kinetics and

in

gain

a

our

from

Apart

H-bonding

IS)

some

operating

in

enzyme

to

associates;

force

detail.

structures

some

molecules

alcohols,

e-g,,

of protein

we

greater

of

molecular

important

example,

the

has

understanding

stabilization

influence

alcohols,

H-bonding

significant

and

alcohol

the

to play For

of

associate, of

known

ability

be

understanding

are

reactions,

reaction

comma nly

known

molecular

plays

111

The

structures

H-bending each

chemical

self-associatian

internal

solvents

rates

reactions.

undergo

as

in many

affect

chemical

used

also C43,

polymer

the

blends

161,

A great understand .solvents

deal the

as

technigues

molecular

have of

dielectric calorimetqj

1331,

magneto-optLca1 provided

us

with

1311,

rotationK35j. important

of

problem

inadeguate.

is .still

alcohols,

attempt

[7-12]_

Several-

the IR

120-231,

non-linear

measurements these

information our

detailed

The

lack

of

inert

molecular Raman

dielectric static

polarization

While

to

in

measurements~C301,

dielectric

self-association

an

alcohols

113-191,

[25-283,

thermodynamic

some

of

in

investigate

NMR

pressure

made

reviews

to

e-g-,

relaxation

constant

been

several

applied

alcohols

vapour

1291,

has

association

in

been

dielectric

effect

effort

appeared

association [24j,

of

1321,

C34l

and

atudies on

have

the

knowledge

on

this

detailed

r..

167 information to

the

despite

following

The

(a1 molecular

the

intense

factors

presence a given

for

linear

multimers

(polymers)

cyclic

multimers

of

(b)

Large

ranging

variation

Each

(c-1

to

is capable

lifetimes

are

the

system

information, single same

For

frequency sample

in

may

long

the

show

to

two

i-e,,

lengths

and

the

associates

the

detected

techniques

-OH

spectrum,

different

whose by

that

applied

provide the

alcohol

associates

to be

while

NMR

alcohol

of

study

the

necessarily

example,

chain

lifetimes

detecting

not

of

of

kinds

[363.

different

may

attributed

sizes,

employed

of

two

be

several

various ring

s

sufficiently

Thus

same

1O-5

of

solution

in the

technique

solutions

technique,

of

different

10 -"

from

may

:

simultaneous

associates

efforts,

the

group

the

types

IR of

to

study

same ap@ears

as

spectrum OH

of

a the

stretching

frequencies-

(d)

literature

The

applications

of

different

different

systems

of

difficult

to make

direct

In

order

to

above,

we

have

system

of

alcohols

(n-heptane) It

by

is expected

able

to ~.

on

to

some to

of

applications with

the

of this

conqkrisons

in

among

several kind of

it

of the

same

is

various

difficulties

the

the

investigate

systematically

(pentanols)

involved

Consequently,

comparisons

attempted

gain-direct

often

techniques

alcolhols.

avoid

that

alcohols

results,

outlined

study

the

inert

solvent

selected approach, results-

same

techniques. We

may

be :. ,.

lfi8

In part

I of

temperature various

pentanols

same

mixtures

binary

recently

the

temperature binary

1373 In

dependence

1

of of

the

of pentanols

mixtures

temperature

studies

H NMR

in

to

of

of

part

alcohols,

investigate

at

III we

the

shift

n-heptane

the

has

forms

chemical

of

a low

viscosities

II,

of

OH

mixtures

employing

part

the

the

binary

communication

in

application

of

effect

This

efforts

reported

have

a function

as

C391-

continuing on

Kerr

C381-

cell

appeared

report

we

in n-haptane

Kerr

our

of

dependence

temperature

of

series

this

of

the

same

various

concentrations-

A brief

is

given

of

Binary

here.

solvents c321,

summary

have

been

non-linear

PreViOUS

studies

mixtures

investigated

dielectric

pentanols

1421

have

measured

been

The

1413and

their

by

dielectric

polarization

[403_

Kerr

effect

tetzachloride

reported

in

and

l-pentanol been

1-pentanol

1291

effect

vapour

system

of

effect

electro-dilatometric in carbon

related

on

at

room

of

temperature

pressures

viscositfes

inert

of

some

above

room

study

of

has

pure

temperature

1433.

TIiEORY

It was bonding

of

dependence

found.earlier ethanol while

protons

were

dilution

of

to the

raising NMR

short)

the

the

chemical

its

In

alcohol

by

temperature

applied

the to

'Linear study

the

NMR

OH proton

the

unaffected,

results, was

that

in

was

shAfta

of

C443-

methyl

created In

order

Association the

temperature

it was

addition,

solvents

hydrogen

problem-

and

methylene

shown

similar to

Model'

account (LAM

that effect for - for

The

Linear

several

investigators

results,

e-g.,

of

features

association

only

of

two

types

free

to

of

the

Saika

&pressed

It

protons,

the

F

Ff

Fu

are

the

are

each

from

The

found while chain

chemical

the or

on

shift

of

the

chemical

shift

to

Gutowsky

and

act&ding

shift,

u,

may

be

(1)

Ff"f

+

fractions

fractions

tke

be

bulk

of

may

bound

be

alcohol,

of

leading

fact

that

and

noted

the.develoxxabnt

the

of

the

chemical

PP

Af/A

=

should

calculations to

system.

are

and

related

A,

and

free to

the

protons,

the

free

alcohol,

I

Ff

in

that

Then,

there

multimers)

end

is different

=

of

follow

It

the

assumed

uf.

These

concentrations as

is

that

which

(linear at

tne

:

and P respectively,

Af

found

is

alcohol

bonds

chains

only

molecular

LAM

a given

experimental

u

where

in

alaohols,

the

of

hydrogen

up,

protons,

as

hare.

polymer

monomers-

1481;

is

those

those

free

to

by

experimental

brevity,

relating given

developed

the

of For

etc-

protons

was

explain

assumptions

are

bound the

LAM

basic

are

protons

alcohol

of

the

to

monomers

of

(LAM)

association

alcohols

protons

internal

the

of

One

bound

145-473

molecular

pclymerization salient

Model

Association

the

Fp

that the

to

molar

theory

the

=

(2)

concentrations as

results

activities

(A - Af)/A

of

well

as

shown the

in

are all

.used

the

This

here,

reacting

is

alcohols

due are

:

atiproximately [493_

The

proportional

use:of

the

mole

to

their

fraction

m&ar

concentrations

is mainly

to

facilitate

the

comparisons

and

(2).

with

followed

Af/A

Further

other

by

rearrangement,

=

‘Up

rearrangement

(U

For

the

the

linear

-

linear

i-mer

are

are

eguilibrium

or

the

solution

equilibrium

=

(3)

(A - Af)/Af

it The

formed-

Ai

the

=

is

(4)

assumed

that

equilibria

only

involving

a

=

of for

the (5)

The

monomeris

+ l)/AIAi

.(A1

may

(5)

+ 1

constant

is considered

constants

Ai

concentration

association

Ki If

that

:

model,

+

represents

A1

shown

egns-(1)

I

A1

where

be

of

- +

give5

- a)

association

polymers

particular

(3)

P

it may

d/tap

-

of

q/b

Combination

systems.

to

be

be

assumed

(6)

1501, the

ideal to be

independent

of

i,

hence

(7)

Such

an

assumption

with

similar

polymerization that

is

assumption [461-

considered employed From

reasonabl_e in

egns,(6j

by

comparison

condensation and

(7),

it

may

be

shown

=

Ai

NW, of

A,

the

total

1

Ii

concentration,

concentrations

follows

d--l(A

of

monomers

(8)

may and

be

expressed

in

various

multimers

-.-

+

terms as

:

substitution

l(A1)

A

=

of

(81

+ 2(A2)

+

(91,

get,

into

we

i(Ai)

---

(91

m

A

=

i(A

C

i=l the

Similary,

concentration

(101

JiKi-' IL

of

free

OH,

Af,

is

0

Af

C

=

(11)

(Al)%Ci-1

i=l

The

summation

approximated

series to

eqns,(l2)

A

Af

By

substituting

that

the

,.

and

and (13)

A+/(1

-

=

A+/(1

- AIK)J

hand

side

=

and of

(11)

may

if AlK

=

eqns.(l2)

K

Thus

..

right

in eqns.(lO)

be

c 1 5-e.

AlK)21

(13)

(13)

into

egn-(4)

(A - Af)/(Af)

(12)

is

I$), equal

it may to

2

be

shown

KAf.

(14)

.

~.

I

162 Eqn,(4)

may

also

Substitution

be

rearranged

l/Af

=

of

eqns-(4)

we

rearrangement

to

(l/A)[(U

(15)

(up

al-da the

be

further

shift,

to u may

1 and

slope

of is

It r51,

there

be

been

(up be

=

l/JA

shoulcl and

little

for

monomer

- uf)

very

small

the

chemical

is

Thus

give

In

:

(17)

a straight

several

left

terms

- uf)/SRIW&)

intercept

by

that

the

follows

- [(up

"P

2

noting

neglectedas

(16)

Consequently,

- a)/(~~

suggested

is

line

whose

up.

invostigators

that

521

0.

=

f

Thus

after

- Of)

bvery

to u-

- uf)/JKl

-[(up

and

- a,)3

by

will

represented

u versus

has

close

may

u

A plot

simplified

solution

will be very P numerator i-e-,

compared

- @/(up

- u)/(up

ctup

concentrated

(14)

(151

__-_--___-_--__--__--~~~~

KA=

may

into

+ l]-

0)

-

cjet,

1 -

eon-

iFf)/(ap

-

and

give

knowing

eqn-(la)-

up

"P

from

Knuwing

up

- 4-s

egn-(17), and

Of,

ppm

we-can it

is

(18)

calculate po.ssible

to

of

from

calculate

Af

163

from

egn,(4)_

Once

Af

iaknown,

K may

be

determined

from

eqn-(14)-

If

the

experiments

temperatures, van't

use

Hoff

may

are be

equation,

slope

of

lnK

allows

Several

[/\H)analyses

The

OH

l/T

the

(Bruker

a B-VT-1000

was

varied

from

the

binary

mixtures

of

to

mole

1,000

in

(Aldrich) distilled, purified

presence

were

dried

.used in

to

CDCl3)

facilitaie from

the

of

the

(19)

the

line

whose

in

enthalpy

in

the

change

are

used

measured

223

with

an

temperatures unit,

K.

The

80-MHZ

were The

temperature

concentrations

pentanols

in

NMR

of

n-heptane

ranged

fraction.

(Fisher)

sodium

stored

coaxial

the in

All

hydride

middle the

of

solutions

dried

dark

and

until

IWilm3d

the

with

and

pentanols fractionally

fractions,

NMEt tubes

separation

alcohol

was

wire,

calcium

only

the

C

here

The

various

over

were

dried

to

of

collecting

Carefully

of

n-heptane

the

samples

form

a straight

controller

down

Spectralanalyzed stored

give

were

WP-80)-

by

0.003

integrated

results,

shifts

controlled

from

various

i-

outlined

experimental

313

the

determination

chemical

spectrometer

should

equations

of the

of

( -L1H/R)(l/T)

versus for

made

at

viz,

l_nK=

A plot

conducted

These needed-

Class)

reference

were.

(1% TMS

ilnder investigation-

‘._

164

RESULTS

AND

DISCUSSION

results

The

pentanols

of

are

plottecl

against

and

3);

5);

against

(Fig-G,

OH

chemical

against

with

Fig-9

a)-

in mole

bulk shows

the

the

temperature

(K),

repetition

in

the

presentation

of

results

selected

each

shown

1 shows

constant,

K

(mol

3-pentanol

enthalpy

the

-1

results

1nK

various certain

as

specified

4,

in molarity

versus

In order

the

to

avoid

the

plots,

only

the

temperatures in

the

manifested

by

these

part

General

Fig-1 1-pentanol

(B)

in which

the

and

legend

for

self-association anc!lconcentration

2 shows

various

in two

trends

and

This

specific

is

the

changes

in

pentanols-

parts.

The

common

part

features

followed

details

first

are

hy

the

discussed.

Aspects.

represents in

the

n-heptane

concentrations

lWUUU,

Each

ti given

for

alcohols,

several

specified

Table

discussed

general

of

temperature

(AH)

are

with

second

with

in n-heptane.

(A) deals

at

of

(Fig-1

(Fig,2,

(A)

at

variation

dm3)

of H-bonding

The

A,

here

Kelvin

figure.

Table

for

pentanols

are

in

various

fraytion,

plot

of

concentrations

of

concentration

reciprocal

of

shifts

temperature

concentration

l/A l/2

7,

the

in

curve the

as

OH

chemical

a funation

(mole

fraction,

represents

a given

inset

concentration,

o&

the

figure-.

the

OH

shift of F)

(Hz)

of

temperature with

0.003.5

concentration It may

chemical

(K)

be

shift

for

F Zi

as seen

that

decreased

Tf!ABLT31,

variation in self-assocfation

constxknt

i&n3/mol)

fn

solUtiun5 of 3-pentanof,

Concentration

243 253 263 273 283 288 293 298 303 308 313

(md../dn?)

5.88

6.95

8.09

9.32

82-8 29-4 12-7 6.6 z

103.8 32.3 13.8 6.8 3.8 2.9 2.2 l-7 1.4 1.1 0.9

114.1 36-l 14.6 7-l ;::

181.2 44.5 16.3 7-7 4.1 3.1 2.4 1.8 1.4 1.1 O-9

2-2 l-8 E O-9

2-2 l-7 l-4 l-1 0.9

41ABLE 2. collection various

of

changes

in enthalpy

of H-bonding

pentanols-

Alcohol

/'H

(W

mol+-1

1-psntanol

-37.3

2-pentanol

-34.4

3-pentand

-35.5

t-pentanol

-58.3

(/\BtI for

168 with is

increasing

known

temperature.

that

thereby

high

This

temperature

is

reasonable,

destroys

of

is

also

It

lowering

the

agreement

with

results

obtained

from

examples,

the

Kirkwood

g-factor

(a sensitive

gauge

extent

the

of

decreases

with

monomeric

alcohol

with

our

own

absolute

results

high

dipole which from

the

show 1391

the

decrease

implying

temperatures, moments

are

and

significant

2-pentanol,

trends

to

that

at

smaller

OUI

and

1-pentanol

found that

increasing dominated

have

small

larger

ones

Results also

collectively

the

viscosity

multimers the

1 for

with

with

t-pentanol

as

to

g =

in

multimers

than

For

alcohols

also

mixtures

temperatures,

Spentanol of

is

addition,

viscous

low

general

pure

B decrease

smaller

less

of

in viscosity

that

These are

binP;y

In

in

approaching

constant,

[371-

H-bonds,

parameter

agreement

same

Kerr

temperature

temperature at

the

the

it

techniques-

a number

General

of

of

of

other

temperature,

1531,

studies

also

shift-

H-bonding)

increasing

values

increasing

chemical

some

since

obtained

show

compared

similar in

Fig,3,

The at

concentration

a given

temperature

temperatures (Fig.2)Fig-4 same

and

is

Results

anti 5, features

increasing

is

of

other

It may in

be

that

increasing

the

also

temperature monotonically

minimum ranges

shown

seen

the

OH

is

by

that

OH

shift

F

observed

investigated.

implying

more

for

a number

all

very

the

All

association

share

rapidly

in the with

higher slowly

interesting for

t-pentanol

illustrated

At

shift

of

of

pentanols

C O-2.

is

chemical

results

increases

changes It

OH

are

shift

for

the

the

pentanols

concentration. nor

of

reFressnted

concentration

concentrations

maximum

dependence

to

with note

concentration

aurves at

increase

that md

no

1 0 H 8 H I f

wa

0243

oisl

omn

vsu

1003 0.0

0.1

0.2

0.3

0.4

0.u

0.8

0.7

0.8

0.0

-I

1. 0

kKnEFRMmcM

Fig-l, Teqperature dependence OH chemical shift of 1-pentanol in n-heptane for selected cone:

Fig.2, ConeOH chemkal t-pentanol

dependence of shift of in n-heptane,

460 0

430

H

410

:

390

I P

570 350

Fig,3,Dependence of OH chemical shift of-various pentanole in n-heptane at F = 0,600,

Fig-I, Cone- dependence of OH chemfcal shift of various pentanols at 303 K

168 : higher Kerr of

doncentirtitioneffect

the

Such

results

Kerr

at

constant with

case

values

It

is

aiso

in

obtained

from

energies

or

this

1391-

Therefore,

for

dominate

Ev

1-pentanol

3-pentanol it

and

concentration

results

were

multimers details

with of

Tne related

Kirkwood system,

increasing valaze is

less

plotted

may

be

K,

Fig-6 are

shows

obtained

However,

for

the

case

obtained _'

as

shown

in

< F

however,

possible

of the

curves

P = O-05,

previous

The

formation

multimer.

the

< 0,600)

multimers

case

the

paper

1393-

in

cyclohexane,

increase

in

g value

less

For

F

< O-1,

smaller than

of

The

1-butanol

that

momen.:

a

with the

g

multimers

the

monomeric

1535.

the

variation

temperature, l/A l/2

the

at

each

1373.

< F <

large

maxima

F > O-1,

1 suggesting

find

with

and for

dipole

to

in

of

shows

formed

aga'nst

molarity, results

also

a net

In.order constant,

g-factor

than

per

discussed

concentration

possessing alcohol

were

monomers

K

results

(0,025

that

For

as

293

increasing

(O-100

view

show

values

activation

with

F c O-100,

interpreted

a few

this

the

concentration. at

and

2-pentanol

the

our

in which

viscosity

t-pentanol

supports

t-pentanol

273

the

increase

and

again.2t

latter

at

that

and

absolute

t-pentanol

with

Ev,

the

with

increasing

found

in

consistent

which

of

B were

flow,

at high

3-pentanol for

of

is

with

exception

laboratory

for

and

for

agreement

viscous

0,006)

may

the

general

concentration

> 0.3

(X3) increase

concentration, a minimum

F

a finding

,

where the

from of

the A is

results

of OH

self-association

chemical

shifts

the

bulk

for

2-pentanol,

l-pentanol t-pentanol,

Fig.7.

the

According

and

concentration

in

Similar

3-pentanol.

different to

are

results

eqn-(171,

are

such

a

460 0 H

440 &6

;

400

I F

310

a0

0.2

0.4

0-a

0.0

1:o

MlnE-

0.7 I/A

‘a

0.0

0.5

0.7 l/A

0.0 ‘R

1.1

l-3

(lnr)‘n

Fig.6-Plots of OH chemical shift of 2-pentanol i.f,2 n-heptane against l/A (cone, of A in molarity),

Fig.S,Comparison of cone, dependence of OH chemical shift of various pentanols In n-heptane at 223 K,

03

0.3

1.1

(m@‘R

Fig.7,Plots of OH chemical shift of t-pentanol l/A 92 n-heptane versus (cone, of A in molarity).

Fig-8,Plots of OH chemical shift of I-pentanol &I2 n-heptane versus l/A (cone, of A in molarlty),

170 plot

should

It may

be

seen

a straight

from

to have

appears 1/A1'2

give

assumption the

OH

close

to

lines

deriving

range

have

slopes

been

shift

data

The

are

that

and

the

Intercepts

are

very

is

obtained

concentration of

OH

the in

for

range

chemical

whole

shift

giving in

unigue,

illustrated

against

concentration

range

(up)

the

(a),

the

high

concentration

straight

by

values. P that only one over

in

the

a linear better

The

straight entire

1-pentanol

(F = O-003

to

results

Similar

Fig.7,

for

at

is very

u

l/2

l/A

of

coefficients

temperature,

Pcurve

egn.(l7)1,

analyzed

correlation

each as

data

the

u

slope

view

get

shift in

yielding

line

In

to

obtained

each

change

polymers

chemical

chosen.

t-pentanol

the

yield

that

curves

order

of

program

for

the

[in

regression 0.99,

intercept

to F = 0,55)_

experimerltal from

whose

2-pentanol)

and

in egn-(16)

chemical

the

(for

(corresponds

made

i-e-,

Fig.6

two

= O-45

line

plots

covering

1.000)

are

shown

Fig-a-

Once

up

has

been

self-association calculated

outlined

Representative

results Similar

pentanols.

It

temperature, constant

respect

range

with

the

made

constants %

for .-

the

are

collected

results

are

to

273

constant

is

independence above

273

in egn_(7) the

formation

in Table

1 for

obtained

K

is

at

a given

(K)

273 with

K,

is

almost

in

the

the

concentration-

self-association a

good

all

various

constant

indication

the

be

other

concentration

the

i-e,, of

for

1 that

changing of

may

section.

Below

K.

the

temperature

constant

changing

of

theory

Table

to

313

concentration

assumption

in

from

value

a given

self-association

self-association Therefore,

the

at

earlier

is evident

the

with

temperature

K,

constant,

as

3-pentanol.

determined,

that

self-association

multfmers

are

the

171 approximately

the

experimental at

low

of

is

for

integrated

has

whose been

analysis better

is

(-AH/R),

applied

to

analyze

enthalpy

O-99

(fiY)

regression

and

B-

(5.1

in

Detailed

view

These

the

Raman

two

applied.

are

pentanols should

the

been

has

give

shown

program

data.

The

pentanola-

The

changes

the

slopes

from

collected

in Table

discussion

on

similarities it may

of in of

the

2.

these

tid be

in

a straight

regression

experimental

results, In

is

which

coefficients

are

the

H-bond

correlation

specific

their

2-pentanol

alcohols, in

the

calculated

of

them

all

A linear

the

they

the

to

the

better

at

this

sections,

Aspects,

l-pentanol,

outlinea

and

among discuss

all

of

equation

pentanol

with

been

facilitate

differences to

have

lines,

pentanols

pofnt

for

due

temperatures,

polarized

egn,(l9),

for

each

slope

than

linear

be

low

enthalpy

Hoff

l/T

fits

may

these

recent

in

van't

for

the

that

This

at

concentration

1243,

against

good

suggests

the

changes

the

a plot

gave

To

by

the

by

of K on

applicable.

pentanols,

of

lnK

Such

Fig,9. line

these

of

K)

structures

the

form

plots

dependence

1-pentanol

determine

formation

not

supported

of pure

To

is

extended

a view

beenvalidated

(T < 273

model

formation

The

The

temperatures

studies

has

results,

association

Such

same,

section

apart A,

also

and

from yield

3-pentanol.

showing close

similar values

features for

/\H

as of

172

3.0 03-PEN-mNoL AT-PENTANOL

2.5 2.0 LN(K)

1.5 l-0

-0-s

I 3.15

3.25

a-35

1Tc

Fig-S, van't for solutions

H-bond

Hoff plots of various

formatfon

2-pentanol

(Table

These

2)-

observed the

NMR

similar pentanols

for

technique AH

be

concentration 273

< T

our

Kerr

energies

< 313. effect of

and

that

of

,&H

of

the

dominated

These

are

by

(F > O-5) results

flow

in

[393

of

are

(kJ/mol)

range

for

be

in in and

the

for

the

same

far from

for in

as

the

these high

temperature

range

agreeme

nt with

general

1373

so

imferred

process the

of /\E

In

association

Similar and

the

[54].

it may

mode

-35-S

constant,K,

respectively

H-bonding.

measurements

viscous

and

3-pentanol,

type

region

a_&

xl000

-34-4

is concerned,

v&ues may

(l/K)

-37,3-

values

O-H---O

3.45

of the self association pentanols in n-hegtane.

i-e_,

1-pentanol,

I

activation binary

mixtures-

173

t-pentanol.

(ii)

Tert-pentanol several

The

ways.

shift

for

other

pentanols,

t-pentanol

the

case

is

of

at 313

temperatures

of

for

All

pentanols-

This

viscous

flow

pentanols

The

AH

the

by

2-pentanol

of

In

the

for of

gas

the the

the

the

phase

observed acids.

formation open

ones.

the

Kinetic

of

One

The

latter of

be

dimers point acetic

for

lower

Finally,

K),

the

values

mode

the

same

No

be

acid

more

the

kJ/mole)

the

IR

carboxyliu

reasons for may

the be

acids

were

given

dimebrization that

favourable

acetone

is

determined

and

partially in

of

among

kJ/mole)

of

explanation

of

c393-

1551,

of AH

other

studies

smallest

(-54

are

as

energy

(-58.3

1561-

of

viscosity

a number

may

Pig-4 at

activation

cyclohexane

magnitude

lowest

t-pentanol

the

> 0.1

value

kJ/mole)

the

for

the

t-p?ntanOl

plausible

cyclic

studies

F

of

is

In

223

than

our

is

large

the

not

t-pentanol

(-63

shown

that

the

dimerieation

as

2).

that

in

chemical

The

H-bonding

with

literature

in

trend

accentuated

larger

for

OH

shift

(for

indicate

value

to

studies

of

concentration

/\H

as is

should

same

chemical

(Table

show

for

comparable for

value

the

Fig-3-

Fig-S

if3 consistent which

large

NMR

in

alcohols

(Ev)

for

OH

difference

t-pentanol

system

in

pentanols

of

the

temperature

differences

of

same

the

considerably

other

association

the

the is

these

shown

of

The

other

following as

a given

from

dependence

illustrated

kJ/mole)

obtained

lower

K.

as

magnitude

(-58.3

while

dependence

for

differ

temperature

t-pentanol,

concentration

the

results

the

than

supported 1573.

the by

174

It

is

produces number

apparent

twice of

In

the

from

of

the

With

same

and

cyclic

the

positions

the

the

understood

the

to

the

groups

take

place,

between -OH form

of

-OH

taking up

to

it

the high

the

in

results

relaxation

the

stacking.

The

is

studies

between

i.e., the

for

it

is

assumed

to be

in

its

stable

chair

alternate

one

latter

below

of

the of

stacking

of

of

the

rings

all the to

occurs

H atoms

cyclic

such

latter

H-bonding

the

a

groups,

inhibiting

0 and

the

better such

rotation

For

each

plane

conformation

pentyl

bifurcated

is From

a staggered

rigns.

the

point

free

The

of H-bonding

a model_

that

formation The

t-pentanol

-C2H,-1 without the

assume

cyclohexane.

and

the

to

of

formation

of in

led

case

neighbour's

and

assumed

the

are

resembling

above

allows

2 H-bonds,

viscosity

exist

one

C~(-CEI~

is

as

significant

occupying

for

nearest

groups, part

closely

group

H-bonds

be

we

may

construction

its

arrangement

formation

same

evidences

multimers.

H atoms

(i-e_,

a spatial alkyl

for

for

are

and

for

a trimer

allow

t-pentyl

respect

the

carboxylic

monomer

13 C NMR

the

cyclic

ring

would

with

may 1371

and

0 and

the

there

dominate

- ring

each

model,

the

responsible

information,

Such

rings

ring)

with

of

per

dimers

[163-

possible

trimers

between

with

system,

with on

be

effect

multimers

conformation

of

Kerr

trimers,

cyclic

may

-the available

among

case

H-bonds

multimers

in hexane

cyclic

compared

the

t-pentanol,

cyclic

our

t-butanol

that

of

that

inferred

of

in

cyclic

observed,

case

suggesting

as

number dimers

of /\H

a-bonds

of

dimers,

cyclic

magnitude

of

open

formationof

the

number

higher

dominating

1391

the

the

The

acids,

that

of

the

trim&s, is

also

may

176

consistent

with

the

alcohol

conducted

changes

very

in

slowly

indicating

with

dipole

the

high

that

moment

dominant

of

molecular

for

more

than

H-bond

the

This

ring-

carboxylic

acids

accounting

for

by

as

with

discussed

the

high

of

constant (O-500

S

associate

association for

the

case

earlier,

observed

Kerr

C371-

formation

analogy

this

range

type

be

mode

the

concentration

may

stacking

for

i.e.,

non-dipolar

ring

one

measurements

laboratory

This allow in

effect

this in

I? S 0,800) a low

Kerr

each of

could

magnitude

would

-OH

group

H-bonding

be

the

of AH

in

reason

for

t-pentanol.

In

temperature shift

of

and the

-OH

group

The

association

model-

model

have

that

the

range

(F > O-5)

Application for

of

and the

results

3-pentanol

is

validity and

has

led

of

study

the of

the

chemical

pentanols

to

fit

the

linear

of

and

the

limitations It

discussed, to

temperatures

model

to

mixtures

applicable

high

range

other

of

common

the

high

to

the

has

in

to

been

concentration

(T > 273

multimers

(e-g-, the

hydrogen

and the

rings

1-pentanol,

trends

results

pentanols for

that

similar

the

account

between

show

give

t-pentanol,

To

used

explored

model

applied

K),

determination

of

/\H

H-bonding.

The

the

binary

are

The

been

dependence

for

results

been

shown

has

concentration

n-heptane-

the

1 H NMR

conclusion,

are

and

For

distinctly

a rather

latter

point,

may'be

yield

bonds,

give

trimers)

2:pentanol

are

AH

values

the

case

different

large it

and

dominant

and

the

of from

magnitude

is proposed

within

of that

the j\Hcyclic

H-bonding

important, .>

176

our

Thus,

association selected

of

more

of

molecular

to

be

be

reached.

approach

peatanols

techniques

to provide

being

integrated

by

on

the

detailed

before

same

of

order

conducted

in

to

our

the

applications

of

binary on

the More

understanding achieve

molecular several

mixtures,

alcohols.

a fuller

In

study

information

association

done

the

to

of

this,

more

has

complex

begun problem

work

will

have

the

problem

CalI

experiments

are

Sciences

and

ltiratory.

ACKNOWLEDGELMENTS

This

projected

Engineerfng

was

Research

funded

Council

by of

the

Natural

Canada

(NSERC).

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