lecture 1-2 suvarn_addition to c=o, mo aspects
TRANSCRIPT
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CH222CH222--Organic Chemistry 2Organic Chemistry 2
Wednesdays
&
Fridays11.05 am (sharp) to 12.30 pm
27
Lectures
1.5
h
each
(18
+
22
h)
Includes
problems
solving/
tutorials u zzes
1st quiz
wed
30
Jan
nd th
Mid sem exam 18 Feb
End
sem exam
19
Apr
Suvarn Kulkarni
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•
• God created earth and heaven
• n
• The cabronyl group
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Syllabus
• Addition to CO group, MO • Enols, enolates and reactions
aspects
• Organometallic reagents for
C-C bond formation
• Aldol reaction• Acylation
•
• Conjugate addition reactions
• Chemoselectivity: Oxidation
and reduction
• Stereoselective reactions
• Organo borane and silicon
reagents
• Retros nthetic anal sis
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CH-222 Organic Chemistry II
Reactions and Mechanisms
• Nucleophilic Addition to C=O group: MO aspects,
Hydration and cyanohydrin reaction, thermodynamic Vs.Kinetic control, Organometallic reagents for C-C bond
,
compounds), ortholithiation, transmetallation, metal
halogen exchange, Stereochemistry of nucleophilica on o car ony group, on uga e a on reac ons.
group, carbonyl reactivity, hydrolysis of esters, amides
and nitriles, esterification, transesterification, conversion
o ac n o ac er va ves, ma ng e ones an
aldehydes from esters via weinreb amide and others.
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• Nucleophilic substitut ion at C=O with the loss of carbonyl
oxygen: acetals, cyclic acetals, thioketal, imines, enamines,
re uc ve am na on, a erna ve me o s or am nes
formation, LAH reduction of amides, Strecker synthesis of
amino acids, Wittig reaction
• Enols, enolates and reactions: Alkylation, kinetic and
thermodynamic enolates, Aldol reaction, specific enol
equivalents (lithium enolate, aza enolate, silyl enol ether,
enamines, zinc enolates), Knoevenagel reaction, Perkin
reaction, Reformatsky reactions, Cannizaro reaction, Mannich
reaction intramolecular aldol reaction Ac lation Claisen
condensation, Dieckman cyclization, Conjugate addition of
enolates, Robinsons Annulation
• carbonyl compounds, chemoselective reduction of carbonyl
compounds.
• e rosyn es s : n ro uc on o re rosyn e c ana ys s
• Applications: to solve problems and design routes for synthesis of complex molecules
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Text BooksText Books
Main Text Book: J. Clayden, N. Greeves, S. Warren and P.
o ers, rgan c em s ry , rs ., x or n vers y ress,
2001.
K. P. C. Volhardt and N. E. Schore “Organic Chemistry: Structure and
Function”, 5th Ed., W. H. Freeman and Company, 2007.
L. G. Wade Jr. “Organic Chemistry”. 7th Ed., Prentice Hall, 2009.
T. W. G. Solomons, C.G. Fryhle. “Organic Chemistry”, 9th Ed., Wiley-
India, 2008.
F. A. Carey and R. J. Sundburg, “ Advanced Organic Chemistry, Part A&B”, 5th Ed., Plenum Press, 2007.
Advanced Organic Chemistry : Jerry March
ereoc em s ry o ar on ompoun s: . . e
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• • Marks for attendance
– XX will be awardedif you miss more than
• < 95% = 4• < 90 % = 3
9 lectures • < 85% = 2
• < 80% = 1
• Quiz 10 x 2
• Midsem 30
• Endsem 46
• Attendance 4
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• No late entries in class, pl note the time (11.05 sharp)
Important points before we start
• Will be marked absent i f you arrive after 10 mins
• Cell phones should be on silence mode
• , , ,
• You may ask questions, preferably about the topic• I may not know the answer
• time constraints
• we will find out together
• Open to suggestions – feed back form, constructive
criticism is welcome
• My observation/views on –• General ‘attitude’,
•
Lets have a round of intro
,
• Reco letters,• Copying in any form
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•
4,5 & 6 (relevant
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The Layout of Periodic TableThe Layout of Periodic Table
Lecture slides are courtesy of Oxford University Press
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The Organic Chemist’s Periodic TableThe Organic Chemist’s Periodic Table
Organic Chemist’s language1. Structure and representation of a molecule (static)
2. Description of reaction mechanism (dynamic) (curly arrows)
Why molecules react/ don’t react with each other?
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Organic reaction
• •
molecules
molecules with
dipoles
• Possess the
re uired activation• Orbital overlap
energy• Flow of electrons
• From Nucleophiles to Electrophiles
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Why organic reactions are slow ??
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Organic Reaction
• Interaction between HOMO of a nucleophile and LUMO of
an electro hile leads to a reaction.
• The two partners should be matched with respect to charge-charge attraction and energy and orientation of orbitals
nvo ve
• Nu- may donate e- from a lone pair (e.g. NH2, OH), a π bond
or a si ma bond in reference
• E+ may accept e- into an empty orbital or an antibonding
orbital of a π bond or even a sigma bond in the above
pre erence or er • These antibonding orbitals are of low enough energy if the
bond is olarized e. CO or if it is weak Br
• Nu- (OH, NH2
), E+ (CO, RX), hydrocarbons - not reactive.
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OrbitalsOrbitals ofof NucleophilesNucleophiles andand ElectrophilesElectrophiles
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Filled Nonbonding + Empty NonbondingFilled Nonbonding + Empty Nonbonding
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Filled Nonbonding +Filled Nonbonding + SigmaSigma Antibonding Antibonding
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Filled Nonbonding +Filled Nonbonding + PiPi Antibonding Antibonding
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Pi bonding +Pi bonding + Empty NonbondingEmpty Nonbonding
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Filled pi as nucleophile and sigma star of Br 2 is electrophile
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Comparison of C=C & C=OComparison of C=C & C=O ππ bondsbonds
e = on s t e most mportant unct ona group n organ c c em stry.
Present in aldehydes, ketones, acids, esters, amides and so on.
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The Carbonyl (C=O) GroupThe Carbonyl (C=O) Group
End-on overlap Side-on overlap
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NucleophilicNucleophilic Addition to C=O Addition to C=O
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MOs Involved in theMOs Involved in the NucleophilicNucleophilic Addition to C=O Addition to C=O
Electrostatic attraction
& low energy π* orbital
HOMO
Very stable π orbital
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NucleophilicNucleophilic Addition to C=O Addition to C=O
A curly arrow means actual movement of a pair of electrons
from a filled orbital into an empty orbital
Here the Nu still attacks the C and not the O. This is because of the orbital overlap:
The pi star orbital has a larger lobe is on C and not on O.
The positive charge is neutralized anyway.
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MO Snap ShotsMO Snap Shots
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Example:Example: CyanohydrinCyanohydrin FormationFormation
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BurgiBurgi--DunitzDunitz TrajectoryTrajectory
Why aldehydes react faster than ketones?
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Br is an electro hile or a nucleo hile?
There is no dipole at all!!
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Large HOMOLarge HOMO--LUMO Gap Makes Strong BondLUMO Gap Makes Strong Bond
Bromine is strongly electrophillic !!
Weak sigma bonds Strong sigma bonds
Low LUMO and high HOMO
Low HOMO and High LUMO
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Organic Reaction
• Interaction between HOMO of a nucleophile and LUMO of
an electro hile leads to a reaction.
• The two partners should be matched with respect to charge-charge attraction and energy and orientation of orbitals
nvo ve
• Nu- may donate e- from a lone pair (e.g. NH2, OH), a π bond
or a si ma bond in reference
• E+ may accept e- into an empty orbital or an antibonding
orbital of a π bond or even a sigma bond in the above
pre erence or er • These antibonding orbitals are of low enough energy if the
bond is olarized e. CO or if it is weak Br
• Nu- (OH, NH2), E+ (CO, RX), hydrocarbons - not reactive.
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HydrideHydride NucleophileNucleophile??
Can we use NaH?
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MO PictureMO Picture
Reaction is called as ‘hydride transfer’
It is the BH sigma bond !!!
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Problems
We discussed CN- and hydride transfer
We will discuss organometallics in next lectureLets talk about some neutral Nucleophiles such as water and alcohol
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HydrationHydration
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Formaldehyde is extremely reactive and it is prone to polymerization
No steric hindrance for going from sp2 to sp3
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Extent of hydration
Governing factors
Steric hindrance
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Write mechanism for formation of ketal of acetone or acetonide of ethylene glycol.
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8/11/2019 lecture 1-2 Suvarn_Addition to C=O, MO Aspects
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Cyclopropanone exists as the hydrate in water but
2-hydroxyethanal does not exists as hemiacetal.
Explain why?
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8/11/2019 lecture 1-2 Suvarn_Addition to C=O, MO Aspects
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Write down the structures of all the possible products of NaBH4 reduction.
How would you distinguish between them?
Which of the three carbonyls will be hydrated?
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8/11/2019 lecture 1-2 Suvarn_Addition to C=O, MO Aspects
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Equilibrium with aldehyde
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8/11/2019 lecture 1-2 Suvarn_Addition to C=O, MO Aspects
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Predict the roduct and su est mechanism
IR - No peak between 1600-1800 Cm-1But shows peak betn. 3000-3400 cm-1
CMR
no peak above 150 but shows a peak at 110 ppm
Explain
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8/11/2019 lecture 1-2 Suvarn_Addition to C=O, MO Aspects
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Su est ste s with rea ents and mechanism
O OH