Alicyclic and Aromatic Hydrocarbons

46 question-and-answer flashcards covering definitions, properties, and reactivity of alicyclic and aromatic hydrocarbons.

What is an alicyclic hydrocarbon?

A compound that is both aliphatic and cyclic, containing one or more all-carbon rings, yet is not aromatic.

Do alicyclic hydrocarbons show aromatic behavior?

No, they do not exhibit aromatic behavior.

What are the three types of alicyclic hydrocarbons based on saturation?

Cycloalkanes, cycloalkenes, and cycloalkynes.

What is a cycloalkane?

A saturated alicyclic hydrocarbon whose ring contains only single bonds.

Give an example of a cycloalkane.

Cyclopropane.

What is a cycloalkene?

An alicyclic hydrocarbon with at least one double bond in the ring.

Give an example of a cycloalkene.

Cyclopentene.

What is a cycloalkyne?

An alicyclic hydrocarbon with at least one triple bond in the ring.

What is the general formula for cycloalkanes?

CnH2n.

What is the general formula for cycloalkenes?

CnH2n−2.

What is angular tension (angle strain)?

Strain produced when bond angles in a ring deviate from the ideal tetrahedral angle of 109.5°.

Why are small cycloalkanes like cyclopropane more reactive?

They possess high angle strain from compressed bond angles.

Why are cycloalkenes more reactive than cycloalkanes?

They have both angle strain and reactive π bonds.

Compared to alkanes, what is a physical property of cycloalkanes?

Cycloalkanes have higher melting and boiling points than their open-chain alkanes.

What intermolecular forces hold cycloalkanes and cycloalkenes together?

Van der Waals forces (dispersion forces).

Are cycloalkenes soluble in water?

No, they have very low water solubility.

In what physical state are most cycloalkenes at room temperature?

They are usually liquids.

What is an aromatic hydrocarbon (arene)?

A compound containing a stable, resonance-delocalized, six-carbon ring such as benzene.

What is the molecular formula of benzene?

C6H6.

What is the structural formula representation of benzene?

A six-membered ring with alternating double bonds (or a circle inside a hexagon).

Why is benzene so stable?

Its electrons are delocalized around the ring, giving resonance stabilization.

Who discovered benzene?

Michael Faraday in 1825.

Who proposed the current structure of benzene?

Friedrich August Kekulé in 1865.

Who explained benzene’s resonance and stability?

Linus Pauling in 1930.

What is Hückel’s Rule?

A planar cyclic molecule is aromatic if it possesses 4n + 2 π electrons.

How many π electrons does benzene have?

Six π electrons.

Is benzene aromatic according to Hückel’s Rule?

Yes; with six π electrons, n = 1 satisfies 4n + 2.

Are aromatic hydrocarbons polar or nonpolar?

They are nonpolar.

Do aromatic compounds mix with water?

No; they are immiscible with water.

How do aromatic hydrocarbons burn?

With a sooty yellow flame.

How does substitution affect the boiling and melting points of aromatic hydrocarbons?

More substitution raises boiling points; higher symmetry raises melting points.

What are polynuclear aromatic hydrocarbons?

Aromatic compounds containing two or more fused benzene rings.

Give three examples of polynuclear aromatic hydrocarbons.

Naphthalene, anthracene, and phenanthrene.

What is a heterocyclic aromatic compound?

An aromatic ring containing at least one heteroatom (non-carbon) in the ring.

Give examples of aromatic heterocycles.

Pyridine, pyrrole, furan, and thiophene.

Name three biologically important aromatic compounds.

Phenylalanine, tyrosine, and tryptophan.

Name three aromatic drugs.

Aspirin, acetaminophen, and ibuprofen.

Why do aromatic compounds undergo substitution instead of addition?

Substitution preserves the aromatic resonance and stability of the ring.

What is electrophilic substitution?

A reaction in which an electrophile replaces a hydrogen atom on an aromatic ring.

What is the sigma complex (arenium ion)?

The positively charged intermediate formed during aromatic electrophilic substitution.

What are activating substituents?

Groups that increase ring reactivity and direct incoming electrophiles to ortho/para positions.

Give examples of activating substituents.

−OH, −NH2, and −CH3.

What are deactivating substituents?

Groups that decrease ring reactivity and direct electrophiles to the meta position.

Give examples of deactivating substituents.

−NO2, −COOH, and −SO3H.

What is the difference between electrophilic addition and substitution?

Addition breaks π bonds (typical for alkenes), whereas substitution retains the aromatic ring.

What is the difference between nucleophilic and electrophilic substitution?

Nucleophilic substitution involves attack by a nucleophile (common in alkanes), while electrophilic substitution involves attack by an electrophile (common in aromatics).