Alcohols Flashcards
The alcohol homologous series has the general formula:
CnH2n+1OH
An Alcohol is Primary, Secondary or Tertiary depending on which …..
carbon atom the OH is bonded too
Explain why Alcohols are polar molecules?
Alcohols are generally POLAR MOLECULES due to the electronegative HYDROXYL GROUP which pulls the electrons in the C-OH bond away from the CARBON ATOM.
How do alcohols form hydrogen bonds?
The electronegative oxygen in the polar hydroxyl group draws electron density away from the hydrogen, giving it a SLIGHTLY POSITIVE CHARGE.
This positive charge can attract the LONE PAIRS on oxygen from neighbouring molecule, forming hydrogen bonds.
What are the properties if small alcohols are exposed to water?
When you mix alcohol with water, hydrogen bonds form between the -OH and H2O. If it is SMALL alcohol (e.g. Methanol, ethanol or propan-1-ol), hydrogen bonding lets it mix freely with water-it’s SOLUBLE in water.
What are the properties if large alcohols are exposed to water?
In LARGER ALCOHOLS, most of the molecule is a non-polar carbon chain, so there’s less attraction to the polar H2O molecules. This means that as alcohols INCREASE IN SIZE, their solubility in water DECREASES.
Hydrogen bonds are beneficial to alcohols, explain why?
Alcohols also form hydrogen bonds with EACH OTHER.
Hydrogen bonding is the strongest kind of intermolecular force, so it gives alcohols relatively low volatility (they don’t evaporate easily into gas) compared to non-polar compounds, e.g alkanes of similar size.
-OH can be SWAPPED for a Halogen to make a …..
HALOGENALKANE
Alcohols will react with compounds containing HALIDE IONS (such as NaBr) in a …..
substitution reaction
The HYDROXYL (-OH) group is REPLACED by the HALIDE, so the alcohol is transformed into a
Halogenoalkane
To convert alcohol into a haloalkane the reaction requires an acid CATALYST, such as…
Sulfuric acid (H2SO4)
To make 2-Bromo-2-methylpropane you just need to:…;
Shake 2-methylpropan-2-ol (tertiary alcohol) with sodium bromide and concentrated sulfuric acid at room temperature.
If you react an alcohol with phosphorous pentachloride (PCl5), a chloroalkane is produced. The general equation for this reaction is:
R in this reaction represents the alkane used.
ROH +PCl5 –> RCl + HCl +POCl3
You can make an IODOALKANE from an ALCOHOL by reacting it with PHOSPHORUS TRIIODIDE (PI3). PL3 is usually made IN SITU (within the reaction mixture) by refluxing the alcohol with ‘red phosphorus’ and iodine. This is the general equation:
3ROH + PL3 –> 3RI + H3PO3
If you heat a CARBOXYLIC ACID with an ALCOHOL in the presence of an ACID CATALYST, you get an …
ester
It is called ESTERIFICATION reaction. Concentrated sulfuric or hydrochloric acid is usually used as an acid catalyst.
The general formula reaction for an esterification reaction is:
R-COOH (carboxylic acid) + R-O-H (alcohol) [an equilibrium with H+ arrows] forms RCOOR the ester where the OR attached to the carbon is the alcohol carbon compound attach to the O + water. It is also a condensation reaction as it releases water.
