10/16/24

Question 1

where is the UV vis region

Answer 1

200-800nm

Question 2

what is a hetereocycle

Answer 2

they are cyclic compounds that contain atoms other than carbon

Question 3

what are the rules for aromaticity

Answer 3

all carbons must be sp2 and cyclic, must follow 4n+2 # of electrons

Question 4

what are anti aromatic compounds

Answer 4

compounds that are cyclic, planar, but follow the 4n rule of pi electrons

they are very unstable and hard to make

Question 5

is cyclobutadiene aromatic, anti-aromatic, or non-aromatic

Answer 5

it is anti aromatic because it has 4 pi electrons which is a 4n number

Question 6

is 1,3,5-hexatriene aromatic, nonaromatic, or antiaromatic

Answer 6

it non aromatic because it is not cyclic

Question 7

is cyclopentadiene aromatic, nonaromatic, or antiaromatic

Answer 7

it is nonaromatic, it has a spacer carbon

Question 8

why does the sp3 hydrogen on cyclopentadiene have a pka of 16

Answer 8

when deprotonated, it forms an aromatic intermediate that is very stable (very stable conjugate base means a stronger acid)

Question 9

what is the cyclopentadienyl anion

Answer 9

it is the conjugate base of cyclopentadiene, it is an aromatic intermediate that is very stable so it contributes to the acidity of cyclopentadiene

Question 10

what are two intermediates that form stable aromatic systems

Answer 10

cyclopentadienyl anion and the cycloheptatrienyl cation

Question 11

what is the nitrogen rule for heterocycle compounds

Answer 11

if no hydrogens are attached to the nitrogen, we do not count the lone pair

if there are hydrogens attached, we count the lone pair because it is in the p orbital array

Question 12

why do we not count the lone pair on a nitrogen with no hydrogen

Answer 12

the lone pair is in the sp2 orbital, not the p orbital, it is orthogonal

Question 13

what does it mean when we say the lone pair is orthogonal on pyridine

Answer 13

the lone pair is 90° out from the orbitals and it is not in the p orbital

Question 14

why is pyrrole aromatic? why do we count the lone pair?

Answer 14

in pyrrole, the hydrogen is in the sp2 orbital and the lone pair is pushed to the p orbital meaning it is part of the pi system

Question 15

what are two examples of aromatics in biochem

Answer 15

pyrimidine and purine

Question 16

how do we count the electrons on a heterocycle with oxygen?

Why?

Answer 16

we count 1 of the lone pairs. The oxygen looks sp3 but since aromaticity is so favorable, it rehybridizes to sp2 to form an aromatic structure

Question 17

how do we count electrons in a sulfur containing cyclic compound

Answer 17

we count 1 of the lone pairs

Question 18

what is halogenation for aromatic compounds

Answer 18

it is the exchange of a hydrogen for a halide by using a catalyst

Question 18

for halogenation of an aromatic, why do we need a catalyst

Answer 18

without a catalyst we do not have a strong enough electrophile

Question 18

in the first step of halogenation for a benzene ring, what do we do

Answer 18

we need to make a good electrophile

Question 19

how does Br2 react with FeBr3 in halogenation

Answer 19

it reacts in a Lewis Acid Base reaction

Question 20

what is the lewis acid and base in the first step of halogenation?

Answer 20

the iron catalyst is the lewis acid and Br2 is a lewis base

Question 20

after the lewis acid base reaction in halogenation, what occurs next to create an electrophile

Answer 20

the bromine breaks off and creates Br+ which is a very reactive electrophile

Question 20

what is the intermediate that forms after benzene reacts with the electrophile

Answer 20

an arenium ion that is stabilized by resonance

Question 20

what type of reaction is it when