5.136				SECTION 5
TABLE 5.20		Atomic and Group Refractions
	Group		Mr D				Group		Mr D
H			1.100		N (primary aliphatic amine)				2.322
C			2.418		N (	sec	-aliphatic amine)		2.499
Double bond (C		"C)	1.733		N (	tert	-aliphatic amine)		2.840
Triple bond (C		#C)	2.398		N (primary aromatic amine)				3.21
Phenyl (C	6H 5)		25.463		N (	sec	-aromatic amine)		3.59
Naphthyl (C	10 H	7 )	43.00		N (	tert	-aromatic amine)		4.36
O (carbonyl) (C		"O)	2.211		N (primary amide)				2.65
O (hydroxyl) (O		9H)	1.525		N (	sec	amide)		2.27
O (ether, ester) (C		9O 9)	1.643		N (	tert	amide)		2.71
F (one fluoride)			0.95		N (imidine)				3.776
(polyfluorides)			1.1		N (oximido)				3.901
Cl			5.967		N (carbimido)				4.10
Br			8.865		N (hydrazone)				3.46
I			13.900		N (hydroxylamine)				2.48
S (thiocarbonyl) (C		"S)	7.97		N (hydrazine)				2.47
S (thiol) (S	9H)		7.69		N (aliphatic cyanide) (C			#N)	3.05
S (dithia) (	9S	9S 9)	8.11		N (aromatic cyanide)				3.79
Se (alkyl selenides)			11.17		N (aliphatic oxime)				3.93
3-membered ring			0.71		NO (nitroso)				5.91
4-membered ring			0.48		NO (nitrosoamine)				5.37
					NO	2 (alkyl nitrate)			7.59
						(alkyl nitrite)			7.44
						(aliphatic nitro)			6.72
						(aromatic nitro)			7.30
						(nitramine)			7.51

5.6.2Surface Tension

The surface

tension

of

a

liquid,

,

is

the

force per

unit length

on the surface that opposes

the

expansion

of

the surface area. In the literature the

surface

tensions

are expressed

in

dyn · cm

1

;

1 dyn · cm

1 1 mN · m

1 in the SI system. For the large majority of compounds the dependence

of the surface tension on the temperature can be given as

a

bt

where

a

and

b

are

constants

and

t is

the

temperature in degrees Celsius. The values

of

a and

b

given in Tables 5.16 and 5.18 can be used

to calculate the

values of surface tension for

the

particular

compound

within its

liquid

range.

For

example,

the least-squares constants

for

acetic anhydride (liquid

from

73

to

140

C) are 35.52 and 0.1436,

respectively.

At 20

C,

35.52 0.1436(20)

32.64 dyn · cm

. 1

A compilation of data of some 2200 pure liquid compounds has been prepared by Jasper,

J. Phys.

Chem. Reference Data

1:

841 (1972).

5.6.3Dipole Moments

The permanent dipole moment of an isolated molecule depends on the magnitude of the charge and on the distance separating the positive and negative charges. It is defined as

qi ri

i