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Questions and Answers
What distinguishes aromatic compounds from most other organic compounds?
What distinguishes aromatic compounds from most other organic compounds?
Which process yields aromatic compounds from coal?
Which process yields aromatic compounds from coal?
What is one source of aromatic hydrocarbons?
What is one source of aromatic hydrocarbons?
Why should benzene not be used as a laboratory solvent for prolonged periods?
Why should benzene not be used as a laboratory solvent for prolonged periods?
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Which of the following is a correct systematic name for a mono-substituted benzene?
Which of the following is a correct systematic name for a mono-substituted benzene?
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Which Greek prefixes indicate the positions 1,2, and 1,4 on a benzene ring?
Which Greek prefixes indicate the positions 1,2, and 1,4 on a benzene ring?
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What is a common name for hydroxybenzene?
What is a common name for hydroxybenzene?
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What happens to alkanes during petroleum refining to form aromatic molecules?
What happens to alkanes during petroleum refining to form aromatic molecules?
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What is the primary characteristic that defines an aromatic hydrocarbon?
What is the primary characteristic that defines an aromatic hydrocarbon?
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Which of the following is NOT one of the four aromatic amino acids?
Which of the following is NOT one of the four aromatic amino acids?
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What effect do aromatic compounds typically have on human health?
What effect do aromatic compounds typically have on human health?
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What general property do most aromatic hydrocarbons share regarding solubility?
What general property do most aromatic hydrocarbons share regarding solubility?
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What type of aromatic compound contains atoms of two or more elements in its ring?
What type of aromatic compound contains atoms of two or more elements in its ring?
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Which of the following aromatic compounds burns with a strong sooty yellow flame due to a high carbon–hydrogen ratio?
Which of the following aromatic compounds burns with a strong sooty yellow flame due to a high carbon–hydrogen ratio?
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Are all aromatic compounds volatile?
Are all aromatic compounds volatile?
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What historical use is associated with the term 'aromatic' in organic chemistry?
What historical use is associated with the term 'aromatic' in organic chemistry?
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How is an arene named if the alkyl substituent has fewer than six carbons?
How is an arene named if the alkyl substituent has fewer than six carbons?
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What does the 'ortho' prefix indicate in disubstituted benzenes?
What does the 'ortho' prefix indicate in disubstituted benzenes?
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What is the main reason benzene is less reactive than typical alkenes?
What is the main reason benzene is less reactive than typical alkenes?
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If a compound has an alkyl substituent larger than seven carbons, how is it named?
If a compound has an alkyl substituent larger than seven carbons, how is it named?
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When naming benzenes with more than two substituents, what is the primary rule for numbering?
When naming benzenes with more than two substituents, what is the primary rule for numbering?
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What is the chemical formula for phenyl?
What is the chemical formula for phenyl?
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What happens when bromine reacts with toluene, specifically at the para position?
What happens when bromine reacts with toluene, specifically at the para position?
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Which of the following best describes the structure of benzene?
Which of the following best describes the structure of benzene?
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Study Notes
Aromatic Hydrocarbons
- Aromatic hydrocarbons are unsaturated cyclic hydrocarbons with a stable bonding pattern.
- They are divided into two categories: aliphatic and aromatic.
- Aromatic compounds, unlike aliphatic, are related structurally to benzene.
Importance of Aromatic Compounds
- Aromatic compounds play a crucial role in the biochemistry of living organisms.
- Aromatic amino acids such as Histidine, Tryptophan, Tyrosine, and Phenylalanine are key building blocks of proteins.
- The 5 nucleotides that make up DNA and RNA are aromatic purines or pyrimidines.
- They are also found in the chemical structures of many natural active constituents.
Properties of Aromatic Hydrocarbons
- Some are liquids at room temperature, while others are crystalline solids.
- Most are non-polar due to symmetrical shape.
- They are insoluble in water.
- They are volatile and carcinogenic.
- They burn with a strong sooty yellow flame because of their high carbon-hydrogen ratio.
Types of Aromatic Compounds
- Neutral Homocyclics: Benzene is an example.
- Heterocyclics: These contain atoms of two or more elements in their ring, usually carbon along with nitrogen, oxygen, or sulfur. Pyridine and pyrimidine are examples.
- Polycyclic aromatic compounds: contain multiple fused benzene rings such as naphthalene and anthracene.
Benzene & Aromaticity
- Originally, Aromatic was used to describe fragrant substances like benzaldehyde, toluene, and benzene.
- Now, the term Aromatic refers to compounds containing a 6-membered benzene-like ring with 3 double bonds.
- Benzene has a depressed white blood cell count (Leukopenia) on prolonged exposure and shouldn't be used as a lab solvent.
Sources of Aromatic Compounds
- Simple aromatic hydrocarbons come from coal and petroleum.
- Coal is a complex mixture containing large arrays of benzene-like rings.
- When heated to 1000°C, coal produces volatile products called coal tar which contains benzene, toluene, xylene, naphthalene, and other aromatic compounds.
- Petroleum contains few aromatic compounds but forms them when alkanes are passed over a catalyst at 500°C under high pressure.
Nomenclature
- Mono-substituted benzenes: Named systematically like other hydrocarbons, with "-benzene" as the parent name. For example, C6H5Br is bromobenzene.
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Alkyl-substituted benzenes: Arene nomenclature depends on the size of the alkyl group:
- If the alkyl group is smaller than the ring (6 or fewer carbons), it's named as an alkyl-substituted benzene.
- If the alkyl group is larger than the ring (7 or more carbons), it's named as a phenyl-substituted alkane.
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Disubstituted benzenes: Use prefixes:
- ortho (o) for 1,2 disubstituted
- meta (m) for 1,3 disubstituted
- para (p) for 1,4 disubstituted
- Benzenes with more than 2 substituents are named by numbering the ring starting with a point of attachment.
Stability of the Benzene Ring
- Benzene is more stable than expected based on the double-bond structure.
- This stability is due to electron delocalization across the entire ring.
- This makes benzene less reactive than typical alkenes, undergoing substitution reactions instead of additions.
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Description
This quiz delves into the fascinating world of aromatic hydrocarbons, exploring their unique properties, classifications, and crucial role in biochemistry. Understand how structures like benzene relate to biological molecules and their significance in proteins and nucleic acids.
