Question

1. In a Diels-Alder reaction, electron-withdrawing groups in the dienophile end up preferentially in

the _________ position, and the diene must be in the ____________ conformation.

A) Endo; s-cis C) Exo; s-trans

B) Endo; s-trans D) Exo; s-cis

2.What is the hybridization of the central carbon of allene (1,2-propadiene)? A) sp B) sp2 C) sp3 D) p

3.Which of the following corresponds to the COC bond angle in diethyl ether? A) 60o B) 110o C) 120o D) 180o

4.Which of the following terms best describes the reactive nature of an organolithium reagent?

A) Carbocation B) free radical C) electrophile D) nucleophile E) carbene

Answer 1

1. In a Diels-Alder reaction, electron-withdrawing groups in the dienophile end up preferentially in

the _____Endo____ position, and the diene must be in the _______s-cis_____ conformation.

2. Central Carbon atom has sp hybridisation in 1,2-propadiene while terminal carbons have sp2 hybridisation.

3. Ethers have a tetrahedral geometry in which oxygen is sp3 hybridized. The C−O−C bond angle is 110 degree. C−O bonds are slightly polar & are inclined to each other at an angle of 110 because of electronegativity difference, resulting in a net dipole moment. This bond angle is greater than that of tetrahedral bond angle of 109028′. This is because of the fact that internal repulsion by the hydrocarbon part is greater than the external repulsion of the lone pair of oxygen.

4.C-Li bond in organolithium reagents is highly polarized. So,carbon attracts most of the electron density in the bond and resembles a carbanion. Thus, organolithium reagents are strongly basic and nucleophilic.