Isomerism
Silanes with more than three silicon atoms can be arranged in various ways, forming structural isomers. The simplest isomer of a silane is the one in which the silicon atoms are arranged in a single chain with no branches. This isomer is sometimes called the n-isomer (n for "normal", although it is not necessarily the most common). However the chain of silicon atoms may also be branched at one or more points. The number of possible isomers increases rapidly with the number of silicon atoms. For example:
- Si1: no isomers: silane
- Si2: no isomers: disilane
- Si3: no isomers: trisilane
- Si4: two isomers: tetrasilane & isotetrasilane
- Si5: three isomers: pentasilane, isopentasilane & neopentasilane
- Si6: five isomers: hexasilane, isohexasilane, 3-silylpentasilane, neopentasilane & 2,3-disilanyltetrasilane
- Si12: 355 isomers
- Si32: 27,711,253,769 isomers
- Si60: 22,158,734,535,770,411,074,184 isomers, many of which are not stable
Branched silanes can be chiral. For example 3-silylhexasilane and its higher homologues are chiral due to their stereogenic center at silicon atom number three. In addition to these isomers, the chain of silicon atoms may form one or more loops. Such compounds are called cyclosilanes.
Read more about this topic: Silanes