TOPIC 7 (review) 03Jan2008 - Georgia Institute of...

Notes: D.M. Collard, 2008CHEM2312: Spring 2008

REVIEW

L35

OUTLINE

1. Reactions

2. Spectroscopy and Stereochemistry

3. Preview of Final


REVIEW OF REACTIONSWhile the following schemes group reactions by type of functional group, recognize that functional groups often undergo a certain type of reaction (e.g., substitution, addition, elimination), and react by a certain type of mechanism, based on their nucleophilicity or electrophilicity.

REACTIONS FROM ORGANIC-ISubstitutions (SN), Additions (C=C,C≡C), Eliminations

C C

H C C H

C C H C C OH

H C C Br

H C C CN

H C C I

H C C SR

RO

R'

H C C OTsBr C C Br

HO C C Br

CH2

O

HO C C OH

C C

HBr

Br H

C C

BrBr

Br Br

O

OH

O

3o

SN1 vs SN2

Markov.vs

anti-Markov.

Markov.

vs

anti-Marko

v.

Zaitsev vs anti-Zaitsev

Zaitsev v

s

anti-Zaits

ev

Markov.

syn, anti

C C

HO

H

H C C MgBrGrignard

additions to carbonyls

nucleophilic ring opening


REACTIONS OF AROMATIC COMPOUNDS

R

Hal

NO2

SO3H

O R

H2CR

NO2

CN

Hal

H

OH

carbonyl additon

reactions

Aryl Grignardreagents

Aromatics substitutions

(strong base: Elim-Addo/p EWG: Add-Elim)

COOH

CHR'Br

Williamson ether synthesis

CN addition reactions

R=2o

REACTIONS OF CARBONYL COMPOUNDS AND ACID DERIVATIVES

OC

HRR

H2C

OH

OC

R'R

RC

OH

O

RC

NR'2

O

RC

OR'

O

RC

O

O

RC

Cl

O

R C N

CO

R

R'=H

R

H2C

NR'2

R NH2

R'=H

NR"(OH, NR'''2)C

CC

CRO OR

CRO OH

CHO CN

CHO OH

CR OH

RC

OH

R''' R'''


REACTIONS OF ENOLATES

O

RH

O

R

R

O

R

R

R

R

Nu OH

Nu

O

OEtH

O

OEt

O O

O

OEt

O

EtO

O

OHR

R

O

RR'

O

RR'

O

RBr

nucleophilic substitutions

carbonyladditions

acyltransfers

aldol

[mixed aldol?]

Claisen

[mixedClaisen?]

SYNTHESIS OF AMINES

R C N

R Br

R N3

R NH2

R CH2 NH2

NH(R)2

O

NOH NH2

R CH2 NH(R)2

NR

O

OH

O

N R

O

O

R Br

NHR

1o


REVIEW OF STEREOCHEMISTRY AND SPECTROSCOPY

RECOGNIZING ISOMERS

IsomersCompounds with same molecular formula,

but different structures

Constitutional IsomersDifferent connectivity

StereoisomersSame connectivity, different

three dimensional arrangement

EnantiomersNon-superimposable

mirror images

DiastereomersStereoisomers which are

not enantiomers, includes Geometic Isomers


CHIRALITY: ENANTIOMERS

An object which has a non-superimposable mirror image is chiral (the opposite of chiral is “achiral”). Another test for chirality is to assess whether the object itself has a mirror plane of symmetry or point of symmetry (point of inversion). Molecules can be chiral. Pairs of molecules which are non-superimposablemirror images of one another are called enantiomers. Enantiomers are examples of stereoisomers: molecules which differ only in the spatial arrangement of atoms.

Molecules with a single carbon atom bearing four different substituents can exist as a pair of enantiomers which differ in the arrangement (“configuration”) of these substituents.

The carbon is stereogenic The carbon is a stereocenter

You must be able to recognize when pairs of molecules are identical (superimposable) or entiomers (non-superimposable mirror images)

S:5.1-5Prob 5.30,31,33,

35a,b,f

A

DB C

A

D BC

Designating ConfigurationStereocenters are designated as having either R- or S-configurations….

- Assign priorities to the substituents using the Cahn-Ingold-Prelog system (briefly, atoms are ranked in order of atomic number; if two atoms are identical, the next set of attached atoms is considered).

- View the molecule with the lowest priority (4) substituent pointing away from you.- Trace from highest priority (1) to second priority (2), to third (3)….

Clockwise = RCounterclockwise = S

e.g., F

Br HCl

D

HO CH3H

D = deuterium = 2H;D > H

CH3C(CH3)3 CH(CH3)2 CH2CH3

C(H,H,H)C(C,H,H)C(C,C,H)C(C,C,C)

CH2OH

C(O,H,H)

C(CH3)3

C(C,C,C)

> >>

C CH2

H

C(C,C,H)

C O

H

C(O,O,H)

CH2OH

C(O,H,H)

>> >


Optical Rotation The observed rotation is α

The observed specific rotataion is [α] = α / c·l

where c = concentration in g/mL and l = pathlength in dm (1 dm = 10 cm = 10-1 m)

The observed rotation, α or [α] depends on solvent, temperature and wavelength of the polarized light. Generally the sodium D line is used for the light sorce and the experiment is done at room temperature, 25 °C.

The specific rotation is then noted as

The specific rotation of an optical pure chiral compound is a “property”like melting point or boiling point

The specific rotation of a given sample depends on it “optical purity”

[α] (conc./solvent)25D

Optical Purity Problem: The [α] of the R-isomer of compound A is +100. What is the [α] of the S-isomer? What is the [α] of a equal mixture of the R- and S-isomers (racemic mixture)?

The % excess amount of one enanatiomer over the other is called the enantiomeric excess (ee). e.g., 100 % one enantiomer, ee = 100 %; 50% one enantiomer, 50% other enantiomer, ee = 0 %.

Problem: The [α] of the R-isomer of compound A is +100. The [α] of a certain mixture of R- and S-isomers of compound A is -50 °. What is the ee of this mixture? What is the % R-isomer in this mixture?


Diastereomers

There are four stereoisomers

STEREOISOMERS WITH MORE THAN ONE STEREOCENTER

AB

C

XY

Z

S:5.11-12Prob:5.33,34,

35c-e,41

For a molecule with n stereocenters, there are a maximum of 2n

stereoisomers. Stereoisomers which are not mirror images of each other are called diastereomers.

H3CCO2H

HO

HOH3C

CO2HHO

HO

H3CCO2H

H

H3CH3C

CO2HH

H3C

H

CH3

H

CH3

OHOH

OH OH

Meso Compounds If the sets of substituents on stereogenic centers are identical there will be fewer than 2n stereoisomers.

Compounds with stereogenic centers which are not chiral are called mesocompounds.

Meso compounds possess a point or plane of symmetry

X

XY

ZY

Z

X

XY

ZY

Z

X

XY

YZ

Z

X

XY

YZ

Z

X X

Y

Z

Y

Z


IDENTIFICATION OF ORGANIC COMPOUNDS

1. COMBUSTION ANALYSIS ⇒ EMPIRICAL FORMULAMeasure mass of CO2 and H2O formed by combustion of a known mass of compound; data cited as mass % of each element present.

2. MASS SPECTRUM ⇒ MOLECULAR WEIGHT

3. EMPIRICAL FORMULA, MOLECULAR WEIGHT ⇒ MOLECULAR FORMULAMolecular formula is an integral number of times the empirical formula

4. MOLECULAR FORMULAS; DETERMINATION OF “SODAR”Sum of double bonds or rings (“SODAR”) For C,H,O,N,Hal: “SODAR” = (2#C + 2– #H – #Hal + #N) / 2If SODAR calculated from empirical formula is not a positive integral (or 0), this cannot be the molecular formula.


5. INFRARED SPECTROSCOPYBonds vibrate at characteristic frequencies – absorb irrad\ation in IR region of the electromagnetic spectrum

Wavenumber / cm-14000 600

1700 C=O

1000-1200 C–O

2900 sp3C–H

3100 sp2C–H

3500, O-H

COOH

1600 C=C

5. 13C NMR SPECTROSCOPYFor 13C nuclear magnetic resonance spectra:

(a) the number of peaks ⇒ number of different types of carbon

(b) the chemical shift ⇒ proximity to functional groups

δ / ppm220 0

C O

C C C Hal

150-220

120-150 110-150

10-50

20-80

40-80

C OC

TMS


6. 1H NMR SPECTROSCOPYFor a 1H nuclear magnetic resonance spectrum:

(a) number of signals ⇒ number of different types of proton

(b) integral ⇒ relative number of each type of proton

(c) chemical shift ⇒ proximity to functional groups

CO

OH

δ / ppm12 0

H

C OHC C

HC Hal

H

10-12broad

7-9 5.5-6.5

0.9-1.8

2-4

3.8-5

CO

H TMS

CO

CH

10sharp

2-3C H

CHCl3

(d) coupling ⇒ the number of adjacent protons

CH2 CH3

CCH3

CH3

H

C CH3

CH3

CH3

a b

aba

a aa

X

X

H

H

H

H

Y

X

H

H

H

H

H

H

X

X

H

H

X

H

H

H

H

H


ORGANIC FINAL

ORGANIC FINAL

NEXT LECTURE…..

THE FINAL – WHAT TO EXPECT….

• ACS standardized final

• 70 multiple choice questions

• The final is REQUIRED!

• Your grade on the final exam will be the higher of:

• your raw score (# x 1.5) (max. = 105!)

• your national %ile

• Course grade (out of 700 points):

E1-E5 + HW/HWeb/PRS + (final exam)

(drop lowest)

>87.5% = A; >72.5% = B; >65% = C; >55% = D.


MULTIPLE CHOICE QUESTIONS!

TOPIC 7 (review) 03Jan2008 - Georgia Institute of...

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