Ch 15: Benzene and Aromaticity Flashcards by Nydia Dixon

What is the molecular formula of benzene?

C₆H₆

How well did you know this?

Not at all

Perfectly

What type of hydrocarbon is benzene classified as?

Aromatic hydrocarbon (arene)

How well did you know this?

Not at all

Perfectly

Describe the structure of benzene.

Cyclic, planar structure with alternating single and double bonds

How well did you know this?

Not at all

Perfectly

What is the significance of benzene’s resonance hybrid structure?

All six carbon-carbon bonds are equivalent

How well did you know this?

Not at all

Perfectly

What is aromaticity?

A property that provides extra stability to certain cyclic compounds

How well did you know this?

Not at all

Perfectly

What is Hückel’s Rule for aromaticity?

A molecule is aromatic if it has a fully conjugated, cyclic π-system with (4n + 2) π-electrons

How well did you know this?

Not at all

Perfectly

List the criteria for a compound to be aromatic.

Cyclic
Planar
Fully conjugated
Follows Hückel’s Rule

How well did you know this?

Not at all

Perfectly

What are some examples of aromatic compounds?

Benzene (6 π-electrons)
Naphthalene (10 π-electrons)
Pyrrole (6 π-electrons, including lone pair)

How well did you know this?

Not at all

Perfectly

What distinguishes anti-aromatic compounds from aromatic compounds?

Anti-aromatic compounds have (4n) π-electrons

How well did you know this?

Not at all

Perfectly

How are monosubstituted benzene derivatives named?

By adding the substituent name before ‘benzene’

How well did you know this?

Not at all

Perfectly

What does ‘o-‘ represent in disubstituted benzene nomenclature?

Substituents at 1,2-positions

How well did you know this?

Not at all

Perfectly

What are the physical properties of benzene?

Nonpolar
High boiling points
Poor solubility in water

How well did you know this?

Not at all

Perfectly

What type of reactions does benzene prefer?

Substitution reactions

How well did you know this?

Not at all

Perfectly

What is the general mechanism of Electrophilic Aromatic Substitution (EAS)?

Formation of the Electrophile (E⁺)
Electrophilic Attack
Deprotonation

How well did you know this?

Not at all

Perfectly

What is an example of a reagent used in nitration of benzene?

HNO₃/H₂SO₄

How well did you know this?

Not at all

Perfectly

What are heterocyclic aromatic compounds?

Compounds containing atoms other than carbon in the ring

How well did you know this?

Not at all

Perfectly

Give an example of a heterocyclic aromatic compound.

Pyridine (C₅H₅N)
Pyrrole (C₄H₅N)

How well did you know this?

Not at all

Perfectly

What are Polycyclic Aromatic Hydrocarbons (PAHs)?

Larger aromatic molecules with multiple benzene rings fused together

How well did you know this?

Not at all

Perfectly

Provide an example of a PAH.

Naphthalene (C₁₀H₈)
Anthracene (C₁₄H₁₀)

How well did you know this?

Not at all

Perfectly

What is the bond length of C–C in benzene?

1.39 Å

How well did you know this?

Not at all

Perfectly

Fill in the blank: A molecule is aromatic if it has a _______ π-system.

fully conjugated, cyclic

How well did you know this?

Not at all

Perfectly

True or False: Benzene undergoes typical alkene addition reactions.

False

How well did you know this?

Not at all

Perfectly

What type of structure does benzene have?

Hexagonal ring structure

How well did you know this?

Not at all

Perfectly

What hybridization do the carbon atoms in benzene exhibit?

sp² hybridized

How well did you know this?

Not at all

Perfectly

What are the delocalized electrons in benzene responsible for?

Aromatic stability

How is benzene represented in terms of resonance?

By two resonance structures

What rule determines if a compound is aromatic?

Hückel’s Rule

What is the formula for Hückel’s Rule?

4n + 2 π-electrons

What are the four criteria for a compound to be considered aromatic?

* Cyclic Structure * Planarity * Conjugation * Hückel’s Rule (4n + 2 π-electrons)

What type of compounds are exceptionally stable due to delocalized π-electrons?

Aromatic compounds

What defines anti-aromatic compounds?

Conjugated systems that fail Hückel’s rule

What is the bond length in benzene compared to single and double bonds?

Intermediate between 1.54 Å and 1.34 Å

What is the first step in the mechanism of electrophilic aromatic substitution (EAS)?

Generation of the Electrophile

What happens during the attack on the benzene ring in EAS?

Creation of a carbonium ion

List the types of electrophilic aromatic substitution (EAS) reactions.

* Halogenation * Nitration * Sulfonation * Friedel-Crafts Alkylation and Acylation

What are electron-donating groups (EDGs)?

Groups that increase electron density on the ring

Give examples of electron-withdrawing groups (EWGs).

* Nitro (-NO₂) * Carbonyl (-C=O) * Halogens (e.g., -Cl)

What is a heteroaromatic compound?

An aromatic compound containing heteroatoms

Name a heteroaromatic compound containing nitrogen.

Pyridine

What is the characteristic of anti-aromatic compounds?

Highly unstable due to 4n π-electrons

Fill in the blank: A compound that does not have a fully conjugated π-system or is not planar is considered _______.

Non-aromatic

What leads to extra stability in benzene?

Aromatic stabilization

What is the relationship between the number of π-electrons and aromaticity in benzene?

Benzene has 6 π-electrons and is aromatic

What type of hybridization do the carbon atoms in benzene undergo?

sp² hybridization

What is the term for the special kind of bonding in benzene that allows for electron delocalization?

Delocalization

What is the approximate bond length of C-C bonds in benzene?

1.40 Å

What is the stability of benzene attributed to?

Aromatic stabilization

What rule must aromatic compounds satisfy regarding π-electrons?

Hückel's Rule (4n + 2 π-electrons)

What is the value of n for benzene in Hückel's Rule?

What is a key requirement for a compound to be classified as aromatic?

Planarity

What are the characteristics of anti-aromatic compounds?

Conjugated system with 4n π-electrons, unstable

What is the first step in the mechanism of Electrophilic Aromatic Substitution (EAS)?

Formation of the Electrophile

What is an example of an electrophile in the nitration of benzene?

Nitronium ion (NO₂⁺)

What is the positively charged intermediate formed during EAS called?

Sigma complex or arenium ion

What type of reaction introduces a nitro group to the benzene ring?

Nitration

What effect do electron-donating groups (EDGs) have on the reactivity of the benzene ring?

Increase electron density, making it more reactive

What positions do EDGs generally direct substitution to?

Ortho and para positions

What are examples of electron-withdrawing groups (EWGs)?

*Nitro (-NO₂)* *Carbonyl (-C=O)* *Cyano (-CN)* *Halogens (Cl, Br, I)*

How do halogens behave as substituents on a benzene ring?

Weakly electron-donating, directing substitution to ortho and para positions

What is a characteristic of pyridine as an aromatic compound?

Electron-poor due to nitrogen atom

What is the structure of furan?

Five-membered ring with one oxygen atom

What makes thiophene aromatic?

Presence of sulfur atom donating electron density through resonance

What is the difference between anti-aromatic and non-aromatic compounds?

Anti-aromatic compounds have conjugation but fail Hückel's rule; non-aromatic compounds lack conjugation or are non-planar

What are biologically important aromatic compounds mentioned?

* Morphine * TNT * Vitamin E * Dopamine * Happy Hormones * Vitamin B1 (thiamin) * Vitamin B2 (riboflavin) * Vitamin B3 (niacin) * Vitamin B9 (folic acid) * Vitamin K * Vitamin B6 * Histamine * Melamine

What is the purpose of Frost circles in relation to molecular orbitals?

Frost circles help to predict the shapes and energies of molecular orbitals and explain the 4n + 2 rule.

What does the 4n + 2 rule indicate about aromatic compounds?

Aromatic compounds will always have an odd number of electron pairs.

What is the stability of benzene attributed to?

The stability of benzene is attributed to its aromatic nature.

What characterizes benzenoid polycyclic aromatic hydrocarbons?

They consist of molecules having two or more benzene rings fused together.

What are derivatives of purine and pyrimidine essential for?

They are essential parts of DNA and RNA.

True or False: Non-planar (4n + 2)p annulenes are considered aromatic.

False

What type of compounds are fullerenes classified as?

They are classified as useful aromatic compounds.

Fill in the blank: Frost circles help explain the _______ rule.

4n + 2

What are the characteristics of non-planar (4n)p annulenes?

They are antiaromatic.

What is the significance of the number of bonding orbitals in aromatic compounds?

The number of bonding orbitals is always an odd number.

List the vitamins that are classified as biologically important aromatic compounds.

* Vitamin B1 (thiamin) * Vitamin B2 (riboflavin) * Vitamin B3 (niacin) * Vitamin B9 (folic acid) * Vitamin K * Vitamin B6

What is the structure of aromatic compounds generally like?

They are planar and cyclic.

True or False: Aromatic compounds can have an even number of electron pairs.

False

What does the term 'benzenoid' refer to?

It refers to compounds that contain benzene rings.

What are some examples of biologically important aromatic compounds?

* Morphine * Dopamine * Vitamin E * Histamine * Melamine

Ch 15: Benzene and Aromaticity Flashcards

(79 cards)