10/16/24 Flashcards
where is the UV vis region
200-800nm
what is a hetereocycle
they are cyclic compounds that contain atoms other than carbon
what are the rules for aromaticity
all carbons must be sp2 and cyclic, must follow 4n+2 # of electrons
what are anti aromatic compounds
compounds that are cyclic, planar, but follow the 4n rule of pi electrons
they are very unstable and hard to make
is cyclobutadiene aromatic, anti-aromatic, or non-aromatic
it is anti aromatic because it has 4 pi electrons which is a 4n number
is 1,3,5-hexatriene aromatic, nonaromatic, or antiaromatic
it non aromatic because it is not cyclic
is cyclopentadiene aromatic, nonaromatic, or antiaromatic
it is nonaromatic, it has a spacer carbon
why does the sp3 hydrogen on cyclopentadiene have a pka of 16
when deprotonated, it forms an aromatic intermediate that is very stable (very stable conjugate base means a stronger acid)
what is the cyclopentadienyl anion
it is the conjugate base of cyclopentadiene, it is an aromatic intermediate that is very stable so it contributes to the acidity of cyclopentadiene
what are two intermediates that form stable aromatic systems
cyclopentadienyl anion and the cycloheptatrienyl cation
what is the nitrogen rule for heterocycle compounds
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
why do we not count the lone pair on a nitrogen with no hydrogen
the lone pair is in the sp2 orbital, not the p orbital, it is orthogonal
what does it mean when we say the lone pair is orthogonal on pyridine
the lone pair is 90° out from the orbitals and it is not in the p orbital
why is pyrrole aromatic? why do we count the lone pair?
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
what are two examples of aromatics in biochem
pyrimidine and purine
how do we count the electrons on a heterocycle with oxygen?
Why?
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
how do we count electrons in a sulfur containing cyclic compound
we count 1 of the lone pairs
what is halogenation for aromatic compounds
it is the exchange of a hydrogen for a halide by using a catalyst
for halogenation of an aromatic, why do we need a catalyst
without a catalyst we do not have a strong enough electrophile
in the first step of halogenation for a benzene ring, what do we do
we need to make a good electrophile
how does Br2 react with FeBr3 in halogenation
it reacts in a Lewis Acid Base reaction
what is the lewis acid and base in the first step of halogenation?
the iron catalyst is the lewis acid and Br2 is a lewis base
after the lewis acid base reaction in halogenation, what occurs next to create an electrophile
the bromine breaks off and creates Br+ which is a very reactive electrophile
what is the intermediate that forms after benzene reacts with the electrophile
an arenium ion that is stabilized by resonance
what type of reaction is it when
