This document provides information on silicones and boron hydrides. It discusses the properties and applications of silicones, including their resistance to heat and chemicals, water repellency, electrical insulation, and strength. It also summarizes the classification of boron hydrides into three series and describes diborane as the most important boron hydride. The structure of diborane is explained, noting that it has an electron deficient structure and that its bonds involve both two-center two-electron bonds and three-center two-electron "banana" bonds between the boron and hydrogen atoms.

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3. • Depending on the length of the chain and
nature of groups attached to the chain silicones
are obtained in many forms.
• Obtained in the form of oils,fluids,resins or as
rubbers.

4. Properties of silicones

5. • Resistant to heat - used in applications where
organic materials would melt or decompose -
oxidation and most chemicals.
• Strong water repellents – silicone fluids-
Silicone chain surrounded by organic side
groups- shoe polish ,car polish.
• Good electrical insulators – silicone oils and
silicone resins-used as dielectric insulating
material in high voltage transformers.

6. • Non-stick properties- silicone resins
• Anti- foaming properties- beer making,textile
dyeing etc.
• Strength & inertness – stable Si-O-Si-O-Si
skeleton and high strength of Si-C bond.
• Lubricating property –Methyl silicones.
• Elastic property- Silicone rubbers-electrical
insulators –vulcanisation yield hard rubber

7. Boron Hydrides
• Also known as boranes.
• Classified into three.
• BnHn+2 series , Closo boranes
• BnHn+4 series ,Nido boranes.
• BnHn+6 series, Arachno boranes.

8. • The most important hydride of boron is
diborane (B2H6).
• This is a colourless gas.
• This substance is highly unstable at the
room temperature with a foul odour.
• It is highly toxic.
• This substance will ignite rapidly at room
temperature.

9. STRUCTURE OF DIBORANE

10. • It is an electron deficient species.
• Total 14 electrons are reqired for the formation of normal covalent
bonds.
• But there are only 12 valence electrons.
• Three from each boron atom and six from six hydrogen atoms.
• Four hydrogens and two borons are in the same plane.
• Two bridging hydroens are in a plane perpendicular to the other
atoms in the molecule.
• This restricts the rotation between two boron atoms.

12. • Terminal four hydrogens are alike and and are called two
centre two electron( 2c-2e) bonds.
• The two bridges involve four electrons.
• One from each boron atom and one from each hydrogen
atom.
• Each BHB bridge bond is 3c -2e bond.
• Each diborane has two such 3c-2e bonds or banana bond.

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