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Questions and Answers
Which type of hybridization is exhibited by each carbon atom in pyrrole?
Which type of hybridization is exhibited by each carbon atom in pyrrole?
How many nitrogen atoms are present in an imidazole molecule?
How many nitrogen atoms are present in an imidazole molecule?
In imidazole, how many electrons does the sp2-hybridized nitrogen atom in the double bond contribute to the aromatic system?
In imidazole, how many electrons does the sp2-hybridized nitrogen atom in the double bond contribute to the aromatic system?
What type of bond does the second sp2-hybridized nitrogen atom in imidazole have?
What type of bond does the second sp2-hybridized nitrogen atom in imidazole have?
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How many lone pairs does the sp2-hybridized nitrogen atom in pyrrole contribute to the p orbital?
How many lone pairs does the sp2-hybridized nitrogen atom in pyrrole contribute to the p orbital?
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Where are the bases covalently attached in nucleic acids?
Where are the bases covalently attached in nucleic acids?
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Which nitrogenous base is composed of two nitrogen-containing heterocycles, imidazole, and pyrimidine?
Which nitrogenous base is composed of two nitrogen-containing heterocycles, imidazole, and pyrimidine?
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In DNA, what is the sugar component that replaces the hydroxyl group at the 2'-position with a hydrogen?
In DNA, what is the sugar component that replaces the hydroxyl group at the 2'-position with a hydrogen?
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Which nitrogenous base is 5-methyluracil?
Which nitrogenous base is 5-methyluracil?
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Which nitrogenous base has a purine structure and exists as the 'carbony' tautomer?
Which nitrogenous base has a purine structure and exists as the 'carbony' tautomer?
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What type of orbital is involved in pyrimidine's sp2 hybridization?
What type of orbital is involved in pyrimidine's sp2 hybridization?
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Which aromatic compound has nitrogens that are both sp2-hybridized and contribute electrons to the aromatic system?
Which aromatic compound has nitrogens that are both sp2-hybridized and contribute electrons to the aromatic system?
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What type of orbital does the nitrogen atom in pyrrole contribute its lone pair electrons to the aromatic system?
What type of orbital does the nitrogen atom in pyrrole contribute its lone pair electrons to the aromatic system?
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How many !electrons are there in the aromatic system of imidazole contributed by the nitrogen atom not involved in a double bond?
How many !electrons are there in the aromatic system of imidazole contributed by the nitrogen atom not involved in a double bond?
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In pyrrole, how many !electrons does each sp2-hybridized carbon contribute to the aromatic system?
In pyrrole, how many !electrons does each sp2-hybridized carbon contribute to the aromatic system?
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Which heterocycle has a lone pair of electrons on nitrogen in an sp2 orbital?
Which heterocycle has a lone pair of electrons on nitrogen in an sp2 orbital?
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Which compound has a delocalized lone pair of electrons in a p orbital perpendicular to the ring?
Which compound has a delocalized lone pair of electrons in a p orbital perpendicular to the ring?
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What type of hybridization do both nitrogens have in imidazole?
What type of hybridization do both nitrogens have in imidazole?
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Which of the following nucleotides is a purine with a bicyclic structure?
Which of the following nucleotides is a purine with a bicyclic structure?
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In RNA, which base replaces thymine in DNA?
In RNA, which base replaces thymine in DNA?
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Which nucleotide base is not found in DNA?
Which nucleotide base is not found in DNA?
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Which type of structure do adenine and guanine nucleotides exhibit?
Which type of structure do adenine and guanine nucleotides exhibit?
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What type of rings do cytosine, thymine, and uracil contain?
What type of rings do cytosine, thymine, and uracil contain?
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Which of the following nucleotide bases are not heterocyclic?
Which of the following nucleotide bases are not heterocyclic?
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Which molecular biology topic will Dr. Mark Carlile cover in Week 25?
Which molecular biology topic will Dr. Mark Carlile cover in Week 25?
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What advice does Dr. Carlile give to students regarding studying biological subjects?
What advice does Dr. Carlile give to students regarding studying biological subjects?
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Which institution offers the Royal Institution Christmas Lectures that are recommended by Dr. Carlile?
Which institution offers the Royal Institution Christmas Lectures that are recommended by Dr. Carlile?
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What topic is covered in the Royal Institution Christmas Lecture titled 'Where do I come from?'
What topic is covered in the Royal Institution Christmas Lecture titled 'Where do I come from?'
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If a molecule has sp²-hybridization, what geometric shape does its electron domain arrangement resemble?
If a molecule has sp²-hybridization, what geometric shape does its electron domain arrangement resemble?
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Which of the following nitrogenous heterocycles is found in the structure of imidazole?
Which of the following nitrogenous heterocycles is found in the structure of imidazole?
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What type of hybridization is exhibited by the carbon atoms in pyrrole?
What type of hybridization is exhibited by the carbon atoms in pyrrole?
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How many pi electrons does each sp2-hybridized nitrogen atom in imidazole contribute to the aromatic system?
How many pi electrons does each sp2-hybridized nitrogen atom in imidazole contribute to the aromatic system?
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In purine, what are the hybridization states of both nitrogen atoms?
In purine, what are the hybridization states of both nitrogen atoms?
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What type of orbital does the sp orbital in pyrimidine contain?
What type of orbital does the sp orbital in pyrimidine contain?
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How many nitrogen atoms are present in an imidazole molecule?
How many nitrogen atoms are present in an imidazole molecule?
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Describe the aromatic compound formed by purine.
Describe the aromatic compound formed by purine.
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Which purine base is a stronger base than purine and protonates at N-1 only?
Which purine base is a stronger base than purine and protonates at N-1 only?
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Which nitrogenous base exists as the 'carbony' tautomer?
Which nitrogenous base exists as the 'carbony' tautomer?
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In purine, where does guanine attach to the base?
In purine, where does guanine attach to the base?
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What type of orbital do both nitrogens in purine contribute to the aromatic system?
What type of orbital do both nitrogens in purine contribute to the aromatic system?
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Study Notes
Pyrrole and Imidazole
- Pyrrole and imidazole are five-membered, nitrogen-containing heterocycles with six !electrons, making them aromatic compounds.
- In pyrrole, each of the four sp2-hybridized carbons contributes one electron, and the sp2-hybridized nitrogen atom contributes two electrons from its lone pair, which occupies a p orbital.
- Imidazole has two nitrogen atoms in a five-membered, unsaturated ring, with both nitrogens being sp2-hybridized.
- One nitrogen in imidazole is in a double bond, contributing one electron to the aromatic system, while the other is not in a double bond, contributing two electrons from its lone pair.
Nucleic Acids
- Nucleic acids are composed of heterocyclic (carbon- and nitrogen-containing) aromatic rings, with a variety of substituents.
- The bases of DNA and RNA are adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U).
- Adenine and guanine are purines, with bicyclic structures (two fused rings), while cytosine, thymine, and uracil are monocyclic pyrimidines.
- In RNA, the thymine base is replaced by uracil.
- Nucleosides are formed when the bases are covalently attached to the 1 position of a pentose sugar ring.
Purine Bases
- The archetype of purine bases is purine, composed of two nitrogen-containing heterocycles – imidazole and pyrimidine.
- Adenine (6-aminopurine) is a stronger base than purine and protonates at N-1 only.
- Guanine (2-amino-6-hydroxypurine) exists as the 'carbony' tautomer.
Tautomerism
- Tautomerism is a reaction involving the intramolecular transfer of a proton.
- Tautomerism can be catalyzed by both acid and base.
- Tautomerism occurs in heterocyclic systems, such as purines, including adenine and guanine.
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Description
Learn about the structures of pyrrole and imidazole, including the hybridization of carbons and nitrogens, as well as the contribution of electrons to the aromatic systems. Understand the differences in the nitrogen atoms' contributions in these heterocyclic compounds.
