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CHM231 Ch.9
| Question | Answer |
|---|---|
| What's the chemical formula for benzene? | C6H6 |
| What are the bond angles in benzene? | All of them are 120 degrees |
| What are the carbon-carbon bond lengths in benzene? | 1.39 Angstroms |
| What is the hybridization of each carbon in benzene? | sp2 |
| Can the structure of benzene be described correctly using Lewis structures? | No |
| What's resonance? | The concept in which two or more equivalent Lewis structures for the same arrangement of atoms (resonance structures) are necessary to describe the bonding |
| How does delocalization of pi electrons affect the total energy of a benzene molecule? | It lowers the total energy |
| What's resonance energy? | The difference in energy between a resonance hybrid with delocalized pi electrons and its most stable hypothetical contributing structures in which electrons are localized |
| What's one way to estimate the resonance energy of benzene? | Compare the heat of hydrogenation of benzene and cyclohexene |
| Is the resonance energy of 1,3 Butadeine smaller or larger than Benzene? | Smaller |
| What's the relation between number of resonance structures and stability of a molecule? | As # resonance structures increases, stability increases |
| What properties must a ring have to be considered aromatic? | Have 1 2p orbital on each atom of the ring, be planar or nearly planar, & have 4n+2 pi electrons in the cyclic arrangement of 2p orbitals |
| What's a heterocyclic compound? | A compound that contains one or more atoms other than carbon in its ring |
| What's a heterocyclic aromatic compound? | A heterocyclic compound whose ring is aromatic |
| What are two examples of heterocyclic aromatic compounds? | Pyridine (contains 1 N) & pyrimidine (contains 2 N's) |
| What is the hybridization of the Nitrogen atom in pyridine? | sp2 |
| What are some examples of aromatic five-membered rings? | Furan, pyrrole, & imidazole |
| What's an electrophilic aromatic substitution? | A reaction in which an electrophile, E+, substitutes for an H on an aromatic ring |
| What's the steps for an electrophilic aromatic substitution? | A reagent generates an electrophile; Electrophile reacts with the ring; Finally a proton transfer occurs & regenerates the aromatic ring |
| How many transition states are there in electrophilic aromatic substitutions? | 2 |
| What is needed for Chlorine & Bromine to react with benzene, and why? | A catalyst; It increases electrophilicity of the halogen |
| What's a benzene ring connected to an NO2 group called? | A nitrobenzene |
| What does Friedel-Crafts Alkylation do? | It forms a new C-C bond between an aromatic ring and an alkyl group |
| What's an acid chloride and what's another name for it? | Acyl chloride; It's a derivative of a carboxylic acid in which the -OH is replaced by a chlorine |
| What are the three locations on a benzene ring in relation to one X-group connected to the ring? | Ortho, meta, para |
| What is the name of a subsituent that causes the rate of a second substitutent to be greater than that of benzene itself? | Activating substituent |
| What is the name of a subsituent that causes the rate of a second substitutent to be lower than that of benzene itself? | Deactivating substituent |
| What are examples of ortho-para directing & activating groups? | Alkyl groups, phenyl groups, & amines |
| What are examples of ortho-para directing & deactivating groups? | Halogens |
| What are examples of meta-directing & deactivating groups? | Nitro groups, aldehyde groups, & esther groups |
| When the second substituent is in ortho or para positions compared to meta positions, is there a better or worse resonance stabilization of the carbocation intermediate? | Better |
| What's a phenol? | A 6-carbon ring that is connected to an -OH group |
| Are phenols or alcohols more acidic? | Phenols |
| Is benzene affected by strong oxidizing agents? | No |
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