Provide the correct name for a benzene derivative (2) Identify false statement (1) Question involving heats of hydrogenation and how they’re related to stability (1) Identify incorrect resonance structure for a given species (3) · Four common examples of resonance exist: Rules on Evaluating the Relative “stability” of Resonance Structures Difference between kinetic
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Provide the correct name for a benzene derivative (2)
Identify false statement (1)
Question involving heats of hydrogenation and how they’re related to stability (1)
Identify incorrect resonance structure for a given species (3)
· Four common examples of resonance exist:
Rules on Evaluating the Relative “stability” of Resonance Structures
Difference between kinetic and thermodynamic product (1)
Why is the ratio of products temperature dependent?
· At low temperature, the energy of activation is the more important factor.
· At higher temperature, most molecules have enough kinetic energy to reach either transition state.
Terminology involving stereoisomers and conformations in conjugated dienes (1)
Reactive dienes and dienophiles (1)
• The two reactions shown above require harsh reaction conditions, but the normal Diels-Alder reaction is favoured by electron withdrawing groups on the electrophilic dienophile and by electron donating groups on the nucleophilic diene.
Dienes Dienophiles
· Several Rules Govern the Diels Alder Reaction related to reactivity of the dienes and dienophile used.
Given a Diels-Alder product, identify the correct starting diene and dienophile (2)
General spectroscopy of benzene derivatives (1)
Identify species as aromatic, non-aromatic, or antiaromatic (3)
Aromatic:
There are some simple rules:
1) The molecule must be cyclic
2) This cycle must be fully conjugated
3) The cycle must be planar – maximizes orbital overlap
4) The electrons must be able to “circulate”- hence must be delocalized no reaction very slowly formed
5) The conjugated cycle must contain 4n+2 π electrons (Huckel’s rule), where n = 0,1,2,3,4,.....
Anti-Aromatic
If the conjugated cycle has only 4n π electrons, it is anti-aromatic, and will either be highly reactive, or will distort in order to violate one of the other rules (1-4).
Aromatic heterocycles and hybridization (1)
o Furan
o Thiophene
Pyrrole much weaker base than pyridine. This is because the lone pair on the N atom is already involved in the aromatic array of p electrons
Pyridine N atom is weakly basic since the lone pair is in an sp2 hybrid orbital.
Aromaticity of ionic species (1)
EAS reactivity trends for benzene derivatives (2)
· Halogenation (proceeds similarly despite halogen present)
· Nitration and Sulfonation
o Unlike the other electrophilic aromatic substitution reactions, sulfonation is reversible.
o Removal of water from the system favours the formation of the sulfonation product.
· Friedel-Crafts Alkylation involves a Lewis Acid AlCl3 to react with the alkyl chloride to form a lewis acid-base complex before carrying out EAS as expected.
· Friedel-Crafts Acylation, the Lewis acid AlCl3 ionizes the carbon-halogen bond of the acid chloride, thus forming a positively charged carbon electrophile called an acylium ion, which is resonance stabilized before carrying out usual EAS.
· Three additional rules to keep in mind in friedel-crafts alkylations
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