Define Heterocyle as it applies to organic molecules.
Cyclic molecules in which one or mroe carbon atoms are replaced by heteratoms - elements other than carbon or hydrogen.
What are two main sub-groups of heterocyclic compounds?
Aliphatic and Aromatic
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Define Heterocyle as it applies to organic molecules. - ANSWER- Cyclic
molecules in which one or mroe carbon atoms are replaced by heteratoms -
elements other than carbon or hydrogen.
What are two main sub-groups of heterocyclic compounds? - ANSWER- Aliphatic
and Aromatic
Explain why pyridine is soluble in water. - ANSWER- First - the ability of pyridine
to accept Hydrogen bonding interactions from water molecules due to the lone
pair of electrons in the nitrogen atom. In addition, the electronegative nitrogen
creates a relatively strong dipole moment in the pyridine molecule, thus making
pyridine a polar compound overall.
Is pyridine more likely to act as an acid or base? Explain. - ANSWER- Pyridine,
like all amines, is a weak base. Amines use the lone pair on the nitrogen atom to
accept protons and thus act as bases.
Name the two main classes of reactions that the pyridine molecule will undergo -
- ANSWER- EAS - Electrophilic Aromatic Substitution
NAS - Nucleophilic Aromatic Substitution
Heterocyclic six-membered rings with two or more N atoms present as a part of
the ring system are known as what type of heterocycles? - ANSWER- Azines
Why are pyrimidines the most biologically important members of the diazene
family of molecules? - ANSWER- Derivatives of pyrimidines are important bases
in the nucleic acids DNA and RNA , namely cytosine, thymine and uracil.
, Name the most important five-membered heterocyclic compounds containing a
single heteroatom substitution and state which element is the heteroatom in
each. - ANSWER- Furan (Oxygen based)
Pyrrole (Nitrogen based)
Thiophene (sulfur based)
What is the most important difference between five and six membered
heterocycles in terms of the bonding a the heteroatom? - ANSWER- The
heteroatom of a five-membered ring contributes two electrons (one lone pair) to
the aromatic pi system of the ring to make the molecule aromatic. This is in sharp
contrast to six membered heterocycles where the heteroatom only contributes
one electron to the aromatic pi system.
Explain why Pyrrole is a weaker base than pyridine, even though both are
aromatic, heterocyclic amines. - ANSWER- This is due to the availability of the
lone pair. In pyridine, the lone pair is available (not part of the aromatic pi system)
to accept an acidic proton. In Pyrrole, this is not the case. Protonation of the lone
pair of pyrrole destroys the aromatic pi system and the special stability of
aromaticity; thus, pyrrole is much less likely to accept an acidic proton on its
nitrogen atom.
Introduction of a nitrogen to the ring of furan, pyrrole, or Thiophene creates a
family of heterocyclic compounds known as what? - ANSWER- Azoles
What is the definition of a fused ring? - ANSWER- In a fused ring system, two (or
more) rings are fused together to form a larger molecule. To be fused means that
each ring shares two (or more) common atoms as a part of the structure of each
ring.
The molecule Indole has what ring fused to the C2-C3 bond of a pyrrole ring? -
ANSWER- Benzene
Adenine and guanine, two of the nitrogenous bases present in DNA and RNA ,
contain what fused ring heterocycle? - ANSWER- Purine
Heterocycles - ANSWER- Cyclic organic molecules in which one or more carbon
atoms are replaced by heteroatoms - elements other than C or H. Largest class of
organic compounds known.
Most common heteroatoms... - ANSWER- O, N, S
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