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Organic Chemistry II Final Exam Material - Coggle Diagram
Organic Chemistry II Final Exam Material
Chapter 21
Introduction to Aromaticity
Benzene = C6H6
Benzene has a low heat of hydrogenation due to stability and lack of static, isolated C=C bonds
In benzene, C-H and C-C bonds are shorter but C-C are all the same despite this; this is as a result of an average of the two resonance structures
a molecule is AROMATIC if it has 4N+2 pi bonds and is planar
molecules with 2,6,10, 14, 18 pi electrons etc. (even number but NOT a multiple of 4)
a molecule is ANTIAROMATIC if it has 4n pi electrons
multiples of 4 are ANTIAROMATIC
Aromaticity in Radicals, Cation, and Anions
heterocyclic molecules are aromatic molecules containing non-carbon atoms such as N,O, P, or S
the lone pair electrons on heterocyclic molecules can either be part of the pi system or not
in atoms with two sets of lone pair electrons (O,S), only ONE pair of them is part of the ring pi system
Atoms that appear to be sp3 hybridized may actually behave as sp2 hybridized atoms
atoms with lone pairs next to pi bonds, only the pi bond counts as part of the ring pi system
General Info:
AROMATIC = 4N+2; ANTIAROMATIC= 4N (multiple of 4);
NON-AROMATIC: not a multiple of 4 but not aromatic
General Info: one pi bond has 2 pi electrons; one lone pair ADDS two 2 pi electrons (3 pi bonds and 2 sets of lone pairs = 10 pi electrons = aromatic; cations do not change the number of pi electrons
Chapter 22
Benzene and its family members can undergo electrophilic substitution (vid 1)
all the C=C reform
Friedel Crafts ALKYLATION includes multiple addition to the ring, rearrangment of cation, and NO reaction with deactivated rings
Friedel Crafts ACYLATION DOES NOT suffer from multiple additions, or rearrangement, but also does NO reaction with deactivated rings; involves use of acid chloride
Halogenation of benzene
Cl and Br need lewis acid catalyst. Including: AlCl3, FeBr3, BF3, HF, and TiCl4
I and F CANNOT be added through halogenation; must use amines, see chapter 23
Cl2/Br2 and a lewis acid are used to create the electrophile for the reaction; ex: Cl-Cl + FCl3 (LA) yields Cl+FeCl4-, where Cl+ is the ELECTROPHILE and FeCl4- acts as a BASE to remove the H to generate the final product
Sulfonation of benzene (conc. H2SO4, reflux)
only reversible reaction in chapter
using SO3 and H2SO4 allows the rate to go faster
Activating groups (vid 3)
activating groups generally direct electrophiles to the ORTHO and PARA positions
activating groups push electron density into the ring by induction and resonance, mainly at these two positions
the family of activating groups include ALL alkyl groups and groups where the atom ATTACHED to the ring has lone pair electrons (O,N) (these groups include delocalization of the lone pair through resonance or conjugation allowing them to donate density to ortho and para)
on an energy diagram (See back), ortho and para have the lowest Ea and tertiary allylic cations
see activating groups with ranking on back
REMEMBER: halogens are DEACTIVATING groups but they direct groups to the ortho/para position; also only deactivating group you can do Friedel Crafts with; energy diagram where benzene has lowest Ea, then ortho para, and then meta has the highest Ea
Deactivating groups (vid 3)
direct the electrophile to the META position; deactivating groups withdraw electron density from the ring via resonance and induction, primarily at this location
this family has atoms attached to the ring that are either partial positively charged or have a positive charge
halogens are an exception to this, see above
energy diagram (see back), meta has a lower Ea than ortho and para
see deactivating group rankings on back
Synthesis with activating and deactivating groups (vid 4)
depending on whether the group attached to the ring is an activator or a deactivator, there are several possible outcomes
1) the two groups can direct to the same spot on the ring and are reinforcing
2) the two groups oppose each other and in this case, the stronger deactivator will dictate the position of the electrophile on the ring
3) the two groups oppose each other and are either both activators or both deactivators and in this case, a mixture will occur
if the two groups are activating, generally the stronger of the two predominates
if one group is activating and one is deactivating, generally the activating group predominates
General Info: Ortho = 1,2 substitution; Meta = 1,3 substitution; Para = 1,4 substitution
Chapter 23
amines are basic due to the lone pair of electrons on N
more basic than alcohols, ethers, water
General info: smaller pKb = stronger base; smaller pKa = stronger acid
conjugation leads to higher pKb
alkyl substituted amines are more basic than NH3 b/c they donate electron density by induction
amides are non basic, poor nucleophiles
Preperation methods (overview)
reduction of imides to amines (ch 16)
aldehyde or ketone + NH2OH + reduction by LiALH4 = oxime
aldehyde or ketone + RNH2 + reduction = imine
aldehyde or ketone + R2NH + reduction = enamine
can use primary, secondary, or tertiary amines
reduction of nitriles to primary amines (ch 18)
CN- is a good nucleophile for SN2 reactions; will react with primary and secondary alkyl halides, which can then be reduced to primary amines
REMEMBER: this includes the ADDITION of ONE carbon!
use of azides (NaN3) does NOT add a carbon
reduction of amides by LiAlH4 (ch 18)
amides are formed from the reaction b/w acid Cl and an amine
NH3 -> primary amine
primary amine -> secondary amine
secondary amine -> tertiary amine
reduction of -NO2 groups (ch 22)
nucleophilic ring opening by ammonia and amines (new, ch 11)
reduction of alkyl azides by LiALH4 (new)
alkylation of ammonia and amines (new)
Reduction of nitro compounds
everything that will reduce C=O to CH2 will do the same to NH2 EXCEPT Wolff Kishner
aromatic and aliphatic nitro compounds can be reduced to amines
[H2/Ni, Pt, or Pd] OR [H+/Fe, Sn, or Zn] can be used
Nucleophilic ring opening
can occur twice
amine acts as a nucleophile opening the ring in an SN2 fashion
Alkylation of NH3 and Amines
problematic because N will continue to attack the electrophile until there are no lone pairs left; SN2 reaction where amine is the nucleophile
Reaction with Amines
common thread is that due to the lone pair electron on N, amines are good nucleophiles
nitrous acid/diazonium salt
AR-N+ triple bond N + ......
H+ -> ArOH
CuCl (Br) -> ArCl (Br)
CuCN -> ArCN
HBF4 (KI) -> ArF (I)
mechanism to get I and F on ring!
H3PO2 -> ArH
ArH -> Ar-N=N-Ar
Hoffmann elimation
involves the cleavage of C-N bonds
R4N+OH- is the starting material
product is an alkene and ammonium salt is a leaving group
Zaitsev = more substituted; Hoffmann = less substituted
There may be a possibility for external or internal double bonds, but the E2 elimination favors anti position (Newman) and for internal double bonds, in the anti position, there is too much steric hinderance. Therefore, an external double bond is formed because it can create the anti position product without steric hinderance
Sandmeyer reaction
replacement of -Cl, -Br, or -CN