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| Melting Point Variation In Heterocyclic Compounds |
Melting point
The temperature at which
a substance transforms into a liquid under the influence of air pressure is
termed its melting point. In this case, there is an equal coexistence of the
liquid and solid phases. In this case, ice cubes begin melting and change from
a solid to a liquid at 0 degrees Celsius. The point at which a material melts
is affected by pressure; this value is typically stated at a standard pressure
of 1 atmosphere (100 kpa).
Heterocyclic compounds
A cyclic compound with a
minimum of two distinct elemental atoms in its ring is referred to as a
heterocyclic compound or a ring structure (s). In organic chemistry, the
production, qualities, and use of these heterocycles are referred to as
"heterocyclic chemistry".
By
switching out a C=C bond with a hetero atom containing a lone pair of
electrons, these heterocyclic compounds are created from benzene. On a cyclic
ring, the most frequent hetero atoms are oxygen (O), nitrogen (N), and Sulphur
(S).
For Example:
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Heterocyclic
compounds include nucleic acid, which is a substance found in the human body
that is in charge of storing and expressing hereditary data. Vitamins are crucial and an indication of a heterocyclic molecule. Heterocyclic compounds are
included in the majority of medicines, insecticides, paints, and polymers.
Factors affecting melting point
·
Ionic
Bonds.
·
Intermolecular
Forces.
·
Shape
of Molecules.
· Size of Molecule.
Melting point variation in Heterocyclic compounds
Usually, organic compounds have a melting point
lower than 200.
1. Increase in Molecular mass increase the
melting point of organic compound, due to large wander walls forces.
2. Hydrogen bonding increase the melting point
due to the electronegative atom. However intramolecular hydrogen bonding decreases the melting point.
3. Bulky groups or functional groups decrease the
melting point due to repulsion distance increase and forces become weak.
4. Large-size branching decreases the melting
point due to repulsion. Large Ring sizes increase the melting point, due to
high molecular weight.
5. Linear long chains have high melting points due to large surface area forces becoming strong.
6. Ionic bond-containing molecules have a high
melting point as compared to covalent bond-containing molecules.
7. The melting is not significantly changed by
substituting a single Sulphur atom (atomic weight 32) for a two-carbon unit
(two carbon and two hydrogen atoms, molecular weight equal to 26). Heterocyclic compounds that contain nitrogen atoms in a ring, as well as hydroxyl or amino groups, are high-melting solids.
8. In contrast, due to the lower molecular
weight of the furan molecules, the replacement of a two-carbon unit with an
oxygen atom (atomic weight 16) decreases the boiling point by around 40 °C (72
°F) because low molecular weight molecules are more volatile.
9. The boiling point rises when a nitrogen atom
or an imino (NH) group add in place of a two-carbon unit.
10. In general, methyl (CH3) and ethyl (C2H5)
groups linked to ring carbon atoms raise the boiling point by roughly 20 to 30
°C (36 to 54 °F) and 50 to 60 °C (90 to 108 °F), respectively.
For example,
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| A |
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| B |
The incoming alkyl group (-R) increases the molecular mass of the derivative in both cases (A & B) but in the (A) molecule there is already a large size molecule, here the other factors also affect the melting point. Now if the –R group is large in size it causes repulsion and decreases the m.p in the (A) molecule but in the (B) molecule it increases the m.p due to increasing molecular weight.
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