2.2 Shape factor (SF)
In order to make the contribution value of the group more accurate, we
introduce the shape factor to describe the influence of the molecular
shape of branched chains, straight chains, and rings on the properties.
The formula of the shape factor is shown in Equation (1) and (2).
where n _H is the number of non-hydrogen atoms;sm is the maximum step;sok is the steps between core atom o and
other non-hydrogen atom k .
2. 3
Atomic connectivity factor (ACF)
The hypothesis of group contribution method is that a group has an equal
contribution value at any molecule. The contribution of group position
is not considered by the traditional group contribution methods.
Therefore, isomers resulted from group position cannot be distinguished
even if multiple level groups were used. Atomic connectivity factor
(ACF) is defined as φk to describe the
contribution of group position on the properties. ACF of a group is
defined by the connection of core atom (o ) with other
non-hydrogen atoms (k ) and the properties of each atom such as
atomic weight (m ), electronegativity (e ), ionization
energy (i ), atomic radius (r ), number of outermost
electrons (o ), number of electrons shell (s ), atom on
aromatic ring (a ) and branched degree (b ). The location
factor was calculated from ACF. The formula for ACF is defined as
Eq.(3). Examples are used to describe
ACF calculation in Supporting
Information (Example.xlsx).
where sok is
the steps between core atom o and other non-hydrogen atomk ; x stands for m, e, i, r, o, s, a , b (b is 1 if the atom is in the aromatic ring and 0 if it is not.).