Quiz on Molecular Orbitals and Pericyclic Reactions in Organic
School
St. John's University**We aren't endorsed by this school
Course
CHE 1210
Subject
Chemistry
Date
Dec 10, 2024
Pages
4
Uploaded by DoctorGerbilPerson139
CHM133 Advanced Organic Chemistry Name: ______________________________________ Date:_______________ TAKE-HOME QUIZ NO. 1 MOT AND PERICYCLIC REACTIONS I. Multiple Choice: Underline the best answer. (2pts each) 1.For 1,3,5,7,9-decapentaene, the no. of Ψmolecular orbitals and the no. of π electrons are _____ respectively. a) 10 Ψ; 10 πe’sb) 10 Ψ; 5 πe’s c) 5 Ψ; 5 πe’s d) 5 Ψ; 10 πe’s 2.Stereochemistry of a pericyclic reaction is determined by: a) mode of activation b) number of πe’s c) both a & b d) number of carbon atoms 3.This molecular orbital of 2,4-hexadiene is the: a) HOMO of the ground state b) LUMO of the ground state c) HOMO of the excited state d) LUMO of the excited state. 4.Which image correctly represents the highest occupied molecular orbital for 1,3-butadiene? a) b) c) d) 5.At the nodal plane, electron density is zero because: a) there is repulsion. b) there is weak overlapping. c) the p-orbitals are distant from each other. d) none of these 6.Which of the following stereochemistry of pericyclic reactions is geometrically difficult. a) disrotatory b) suprafacial c) conrotatory d) antarafacial 7.A molecule with an even number of πbonds will undergo what type of electrocyclic reaction? a) conrotatory, thermal b) conrotatory, photochemical c) disrotatory, thermal d) disrotatory, photochemical 8.The following rearrangement reaction is called: a) Cope b) Claisen c) Diels-Alder d) Kolbe 9.Dienes and dienophiles are involved in: a) electrocyclic reactions b) cycloaddition reactions c) sigmatropic rearrangement d) all of these. 10.In order to be aromatic all bonding molecular orbitals (MO) of a compound must be ...
a)occupied incompletely; there must not be any electron in a destabilizing antibonding or non-bonding orbital. b)occupied completely; there must not be any electron in a stabilizing antibonding or non-bonding orbital. c)occupied completely; there must be at least one proton in an antibonding or non-bonding orbital. d)occupied completely; there must not be any electron in a destabilizing antibonding or non-bonding orbital. 11.Hückel's rule says that a compound must have ____________ to be aromatic. a) 2n + 2π electrons b) 4n + 2π electronsc) 4n + 4π electronsd) 1n + 2π electronsII. True or False. (2pts each) 1. HOMO and LUMO of a π-conjugated system are of the same orbital symmetry. _______________ 2. HOMO is always of lower energy than LUMO in all conjugated π-e systems. __________________ 3. Photochemical activation occurs through excited state of its LUMO. ___________________ 4. In electrocyclic reaction, the terminal carbon p-orbitals must rotate 90oto close the ring. _________ 5. In aromatic systems, there are always degenerate orbitals. ___________________ 6. The total number of π& σ bondsin a conjugated π-electron system, will not change when it undergoes pericyclic reaction. _________________________ 7. All pericyclic reactions do not need reagents nor catalysts. _______________________ 8. Pericyclic reactions are reversible reactions ________________________ 9. Both HOMO and LUMO are always involved in all pericyclic reactions. ______________________ III. Classify the type of the following sigmatropic reactions using bracketed classification. Specify whether hydride or alkyl. Example: (x,y)-alkyl shift. (2pts each) 1. ___________________ 2. ____________________ 3. ____________________ II. Classify the following Pericyclic Reactions as electrocyclic, cycloaddition, sigmatropic rearrangement. (2pts each) 1. _____________________ 2. _____________________ 3. _____________________
III. Determine whether each the following is aromatic or not based on a) [4n+2] rule (1 pt) and b) MOT. (2 pts each) 1. 2. 3. III. Answer as Directed: Use the space available below or use additional sheets for your answers. 1. Explain why the following reaction is forbidden under thermal activation but allowed under photochemical activation. Use orbital symmetry to support your answer. (6pts) 2. Draw the molecular orbitals for CH2=CH-CH=CH-CH2:¯ and (a) Indicate the number of nodes and orbital symmetry (b) Label the HOMO and the LUMO in the ground state. (c) Label the HOMO and the LUMO in the excited state (d) Label MOs and MO*s and non-bonding MOs, if any. (10pts)
3. For (cis, trans)-2,4-hexadiene a) Give its structural formula reflecting the indicated stereochemistry. b) What is the stereochemistry of its thermal cyclization reaction? C) Give the product reflecting the correct stereochemistry. (5pts) 4. Explain using: a) Resonance argument and b) Molecular Orbital argument why the lone pair in propenyl anion is delocalized on C1 and C3 but not on C2. (6pts) 5. Determine the stereochemistry of the following sigmatropic rearrangement. Illustrate. (3 pts.)