Question

Can you please answer all of them?

Section B: Free Response (you must show your work for full credit) 1. Draw Frost circle diagrams for each compound shown. Assume that all atoms in the ring are sp2 hybridized. Populate the pi electrons in the corresponding MO's. Identify the compound as aromatic or antiaromatic. (5 pts) 2. What is the Hückel number of pi electrons for the molecule shown below? How many pi electron pairs does it have? Would you expect this molecule to be aromatic, antiaromatic or non aromatic? Explain. (3 pts) 3. Rank the reactivity of the compounds shown below when using a Friedel Crafts alkylation reaction. Make sure you label which is least reactive and most reactive. (5 pts) CH,

Answer 1

1.

Anti-bonding ... Non-bonding Bonding The given molecule contains only 1 pi bond and mo negative charges. Hence number of elections available is 2. These elections are filled in bonding Molecular Orbital. Hence, it is aromatic. - Antibonding f... I ---- Nen-bonding -Bonding The given molecule contains 2 pi bonds and no negative charge (the charge on oxygen is not delocalised on eing). Hence, the number of electrons available are 4. These electrons are filled in bonding molecular orbital. Hence, it is aromatic.

2.

Huckel's number of pi electrons means the electrons which satisfy huckel's rule. This include all the electrons that are in delocalisation in the given molecule.

In our system, 6 pi bonds and 1 lone pair of electron from oxygen are in delocalisation. Since, 6 pi bonds contain 12 (= 6 × 2) electrons and 1 lone pair contains 2 electrons, total number of huckel's pi electrons are 12 + 2 = 14.

Since, it has 6 pi bonds, it will have 6 pi electron pairs.

Also, since huckel's electrons are 14, it follows huckel's rule for aromaticity (4n + 2 pi electrons, where n =3).

3.

In friedel-crafts alkylation, an electrophile attacks the benzene ring. For better reactivity the ring must be electron rich. This means that the ring should contain electron releasing groups.

Electron releasing groups increases the reactivity of friedel-crafts alkylation.

Electron withdrawing groups decreases the reactivity of friedel-crafts alkylation.

In the given compounds,

Br. ENG Br EWG To (B) ENG EDG via I I effect Oz ol EDG rol Lol via tu effect. Br. ENG. NO ENG EDG CH₂ EDG via via +I +I effect effect ENG = Electron withdrawing group. EDG - Electron donating/Releasing group.

Since, all the molecules contain same EWG, we can neglect that for now.

Also, Mesomeric effect is stronger than inductive effect.

So, Molecule D will be most reactive and Molecule B (containing both EWG) will be least reactive.

Now, between molecule A and C, C will be more reactive because it contains 2 EDG and also Br is not directly attached to the ring, so its effect will be less.

Therefore, order of reactivity is D > C > A > B.

4.

4. The given Reaction follows Benzyne Mechanism. HE b C Br. NH₂ LCH₂ concerted Mechanism Нco нсон NH3 at (b) NH3 at (@) NH3 NH -CH3 JH-shift t-shift H NH₂ acha Hot