Chapter 16

Umaimah Kazi
Flashcards by Umaimah Kazi, updated more than 1 year ago More Less
Umaimah Kazi
Created by Umaimah Kazi over 1 year ago
1
0
0

Description

Exam 2
Tags

Resource summary

Question Answer
Discovery of benzene -C:H ratio 1:1 -Molecular formula- C6H6 -Low C:H rations/conjugated/aromatic- has pleasant smell
Addition of bromine to benzene: What catalyst is needed to add benzene? Substitution or addition reaction? When bromine adds to benzene, a catalyst such as FeBr3 is needed. The reaction that occurs is the substitution of a hydrogen by a bromine.
Why does benzene undergo substitution with Br2 while cyclohexene undergoes an addition reaction? -Addition of Br2 to benzene is unfavorable. -It would result in a non-aromatic product. -Addition of Br2 to the double bond is not observed. Screen Shot 2018 06 27 At 7.10.34 Pm (binary/octet-stream)
Resonance energy of Benzene -Benzene does not have the predicted heat of hydrogenation of –359 kJ/mol. -The observed heat of hydrogenation is –208 kJ/mol, a difference of 151 kJ. -This difference between the predicted and the observed value is called the resonance energy. (molar heats of hydrogenation)
Resonance structures of benzene -Benzene is actually a resonance hybrid of the two Kekulé structures. -The C—C bond lengths in benzene are shorter than typical single-bond lengths, yet longer than typical double-bond lengths (bond order 1.5). Screen Shot 2018 06 27 At 7.33.03 Pm (binary/octet-stream)
Structure of Benzene -Each sp2 carbon has an unhybridized p orbital perpendicular to the ring that overlaps around the ring. -The six pi electrons are delocalized over the six carbons.
Failure of Resonance Picture -All cyclic conjugated hydrocarbons were proposed to be aromatic. -However, cyclobutadiene is so reactive that it dimerizes before it can be isolated. -Cyclooctatetraene adds Br2 readily to the double bonds. Screen Shot 2018 06 27 At 7.37.36 Pm (binary/octet-stream)
What are the MO rules for benzene? 1. Six overlapping p orbitals must form six molecular orbitals (MOs). 2. Three will be bonding, three antibonding. 3. Lowest-energy MO will have all bonding interactions, no nodes. 4. As energy of MO increases, the number of nodes increases.
Draw out MOs for Benzene Screen Shot 2018 06 27 At 7.42.41 Pm (binary/octet-stream)
First MO of benzene - is entirely bonding, no nodes -has very low energy because it has 6 bonding interactions and the electrons are delocalized over all 6 carbon atoms
Intermediate MO of benzen -are degenerate (equal in energy) with 2 orbitals are each level -π2 & π3 have one nodal plane (each)
All antibonding MO of benzene -The all antibonding π6* has 3 nodal planes -Each pair of adjacent P orbital is out of the phase in a destructive manner
Describe the energy diagram of benzene - all bonding orbitals are filled "closed shell" -> extremely stable arrangement -6 π electrons fill 3 bonding π orbitals
Draw MO of cyclobutadiene
Show full summary Hide full summary

Similar

Chapter 16 Key Terms
Monica Holloway
Module 3 Study Guide
amatthews1
NASM Chapter 16 Chronic Health Conditions and Physical or Functional Limitations Vocab
Brittany Contrera
Chapter 16 Flash Cards
Antonio Orange
Chapter 16: Political Revolutions in Europe and the Americas
Ashley Green3150
16 The South and the Slavery Controversy 1793-1860
Shari Anderson
Microbiology Exam Three Chapters 14, 15, 16, 17, and 18
Michelle Kimble
Chapter 16 Key Learning, Biology
girlwithnosmile
Cell 11/1 (Chapter 16)
Isabella N
Chapter 16 Gov't Acct
Josh Rondestvedt
Chapter 16 test flash cards
Josh Rondestvedt