Re: Why is it that Isopropyl rubbing alcohol affects water and oil?

a) By 'affects' I think you are referring to the fact that alcohols
   are soluble in both water and oil.

b) The systematic name for isopropyl alcohol is propan-2-ol
   The structure is CH3-CH(OH)-CH3
   It is called rubbing alcohol becuase it is definitely not for
   drinking! Propan-2-ol is commonly used in disinfectant swabs used
   to clean skin before an injection, and many people recognise it
   from this.

OK, why is propan-2-ol (and many other alcohols, for that matter)
soluble in both oil and water?

Water: The -OH part of the molecule closely resembles the HOH structure
of water molecules. In particular, the oxygen atom has a small negative
charge i.e. the charge on the molecule is polarised between the 
negative oxygen atom and the rest of the molecule.

In addition, the hydrogen atom of the -OH group can be partially 
transferred to the oxygen atom of a water molecule, and hydrogen atoms
of water molecules can be partially transferred to the oxygen atom of
the -OH group. This interaction is called hydrogen bonding.

So, water dissolves alcohols because alcohols are polar and capable of
hydrogen bonding.

Oil: The word 'oil' covers a multitude of liquids which are insoluble 
in water. They are hydrocarbons (almost always), and so contain only
hydrogen and carbon - no polarising atoms like oxygen are present.
Because oils are non-polar and cannot hydrogen bond, they are not 
soluble in water.

Alcohols, however, are mostly hydrocarbon. Large parts of alcohol
molecules are just like oils and so are capable of mixing with oils
very nicely. OK, they have a polar -OH group, but this does not affect
their oil-solubility very much.

Pernod: Ever mixed Pernod or other aniseed-flavoured drinks? There are
oils called terpenes in the liquor, which dissolve in 30 % ethanol, the
alcohol in drinks. When you mix Pernod, the alcohol is diluted and the
terpenes are no longer soluble in the resulting 5-10 % ethanol. The
result is that although Pernod itself is clear, it mixes to form a
cloudy drink - made cloudy by precipitated terpenes. Unfortunately,
this doesn't alter the taste.