Saturday, 21 May 2011

Nomenclature and physical properties of some functional groups

I'm far too lazy to copy out those pictures. Will appear on doc. ver.

Nomenclature
Functional group
Example
Preference as suffix
Carboxylic acid
RCOOH
Propanoic acid
Prefix
Suffix
------
-oic acid
Ester
RCOOR'
Ethyl ethanoate
------
-oate
Amide
RCONH2
Propanamide
------
-amide
Aldehyde
RCHO

Methanal
(Formaldehyde)
Oxo-
-al
Ketone
RCOR1
Penta-3-one
Oxo-
-one
Alcohol
ROH
Butan-1-ol
Hydroxy-
-ol
Amine
RNH2
Propan-1-amine
Amino-
-amine
Alkene
C=C
Hex-3-ene
-----
-en-
Note:
1)       In HKDSE we focus on non-substituted amine and amide, so they are primary.
2)       Naming ester: the part -OR1 is names by –yl while R is named by –oate. For the above example both substituent is ethyl group so it's ethyl ethanoate.
3)       The functional group with higher position in the table means it has a high preference as a suffix. For example when a multifunctional compound contains amide and alcohol, say HOCH2CONH2, amide is the suffix, so it is hydroxyethanamide.
4)       Some functional group must exist in the terminal of carbon chain like carboxylic acid, amide and aldehyde, some of them must be in the middle, like ester and ketone.
5)       The =O actually refers to a carbonyl group, so carboxylic acid is a combination between carbonyl and hydroxyl group, and amide is the combination between carbonyl and amide group.
The standard form of nomenclature:
Geometrical configuration – Prefix – Parent chain – Unsaturated Form – Suffix
1)       Prefix: The functional groups with less preference are arranged here in alphabetical order, like 2-bromo-3-chloro….
2)       Parent chain is the longest continuous carbon chain containing function group. The chain with the functional group in suffix is chosen. If there're more than one possible choices, we choose the one with double bond. (We do not discuss the peroxide related function group here.)
3)       Unsaturated form: double bond is represented by –en-, so if there're two double bond the unsaturated form is –dien-
4)       Suffix: the function group with highest preference.
5)       Number assignment must be assigned as 1 at one end of the chain; the number of the functional group at the suffix must be minimized. e.g. it's propan-1-ol instead of propan-3-ol. Also, number assignment is needed only if it is not unique. For example, HOCH2CONH2, it is hydroxyethanamide but not 2-hydroxyethanamide since the first carbon already have four bonds with non-hydride substituent so it must be on the second carbon.
Physical properties
(Note: ID-ID refers to instantaneous dipole-induced dipole attraction, PD-ID refers to permanent dipole-induced dipole attraction, PD-PD refers to permanent dipole-permanent dipole attraction, HB refers to hydrogen bond, r.t. refers to room temperature.)
Functional group
Boiling point
Solubility in water
R (alkane/alkene)
Low since it's non-polar, only ID-ID exist
Insoluble since it's non-polar
RX
Moderate, PD-PD (RX----RX), haloethane is liquid in r.t..
Slightly soluble due to PD-PD between RX and H2O
ROH
High since HB exist (ROH----O in ROH), MeOH is already liquid in r.t..
High due to HB with H2O, MeOH to PrOH is miscible with water at all proportion.
RCHO/RCOR1
Moderate, PD-PD exist between O and the carbon connected to O.
High, HB with H2O, ethanal and propanone is miscible with water at all proportion.
RCOOH
Very high due to dimer formed doubled the size and the intermolecular force.
Very high due to extensive HB with H2O, the first four RCOOH is miscible with water at all proportions.
RCOOR1
High due to PD-PD between C and O, similar to ketone with similar molecular size, note that no HB formed because no H atom is attached to O.
High since it forms HB with H2O.
RCONH2
Even higher than RCOOH since much more HB can be formed.
Very high due to HB formed with H2O
RNH2
Higher than RX, PD-PD between N and H, but N-H is less polar than O-H.
High due to HB with H2O
Note: the general trend is given by:
1)       Boiling point increases as molecular size increase due to increase in intermolecular forces.
2)       Solubility decrease as molecular size increase, carbon compound with very long chain must be insoluble in water no matter what functional groups they have.

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