The
root name is based on the number of C atoms in the ring structures.
The
prefix spiro[x.y] is added where x and y
are the number of atoms in the links as defined below.
The
size of the rings is indicated in square brackets by counting the number of
atoms in the links that make each ring, x and y, excluding the spirocenter.
The number of atoms in the links is listed smallest first, i.e. spiro[x.y] where y
> x
For
substituted spiroalkanes, the rings are numbered starting
on the smallest ringadjacent to the spirocenter.
If that does not resolve the numbering, then the other rules for determining locants are applied in order (i.e. principal functional group, first point of difference, alphabetisation).
STUDY TIP In spiro systems, number the smallest ring first spiro = smallest
Functional group is an alkane, therefore suffix = -ane
The ring structure requires the prefix spiro
The ring structure is C5 therefore root = pent
Excluding the spirocenter, there are two C atoms in each ring =
[2.2]
spiro[2.2]pentane
Functional group is an alkane, therefore suffix = -ane
The ring structure requires the prefix spiro
The ring structure is C8 therefore root = oct
Excluding the spirocenter, one ring has two C atoms and the other
has five C atoms = [2.5]
spiro[2.5]octane
Functional group is an alkane, therefore suffix = -ane
The ring structure requires the prefix spiro
The ring structure is C9 therefore root = non
Excluding the spirocenter, one ring has three C atoms and the other
has five C atoms = [3.5]
There is a C1 substituent = methyl group
The lowest locant (first point of difference) = 5
5-methylspiro[3.5]nonane
Show spirocenter
Functional group is an alkane, therefore suffix = -ane
The ring structure requires the prefix spiro
The ring structure is C9 therefore root = non
Excluding the spirocenter, one ring has three C atoms and the other
has five C atoms = [3.5]