química orgânica i - ualgw3.ualg.pt/~abrigas/qoi0809a1.pdf · 1 w3.ualg.pt\~abrigas qoi 0809 a1 1...

$: Química Orgânica I - UAlgw3.ualg.pt/~abrigas/QOI0809A1.pdf · 1 w3.ualg.pt\~abrigas QOI 0809 A1 1 Química Orgânica I 2008/09 w3.ualg.pt\~abrigas QOI 0809 A1 2 Química Orgânica$
1

w3.ualg.pt\~abrigas QOI 0809 A1 1

Química Orgânica I

2008/09


Química Orgânica I - 2008/09

• Como vai ser?

– Aulas (PT)

– Laboratórios

– Homework

• How should I work– Livros

– Biblioteca

– Internet

– Software/modelos

– Estratégias para o laboratório

– Estratégias para estudar

• Avaliação

– 0 a 20 (30% P + 70 % T); mínimo 9.5 (T and P)

• How it will be?

– Classes (PT)

– Labs

– Homework

• How should I work– Books

– Library

– Internet

– Software/models

– Stratagies for lab

– Stratagy to study

• Evaluation

– 0 a 20 (30% P + 70 % T); minimun 9.5 (T and P)

2


...go Organic

• Organic (C)

• Inorganic

• Organometalic (C-M)


Organic Chemistry

• History

– Ancient history:

• Pharaonic and Graeco-Roman mummies

– myrrh, cassia, palm wine, 'cedar oil'

• Traditional ancient remedies

– "We are trying to bring ancient wisdom and modern science together."

– Mistic times

• Magic

• Alchemy

3


Organic Chemistry

• Modern history:– Vitalism

• 1807- Jöns Jacob Berzelius:

• organic chemistry is the study of compounds derived from biological sources

– The Wöhler synthesis • In 1828 Friedrich

Wöhler synthesized a biological compound, urea, from non-biological sources


Vital Force Theory

Organics compounds hard to purify

Appeared to violate the Law of Definite Proportions

Organic Chemistry problems

Isomerism problem - same molecular formula butDifferent compounds

4


Organic Chemistry

• The Wöhler synthesis of urea (1828)

heatNH4

+ OCN

- H2N C NH2

O

urea

(More serendipity in Chemistry)•Gelignite by Alfred Nobel, •Polymethylene by Hans von Pechmann, who prepared it by accident in 1898 •Low density polyethylene by Eric Fawcett and Reginald Gibson 1933 •Racemization, by Louis Pasteur. •Teflon, by Roy J. Plunkett, •Cyanoacrylate-based Superglue (a.k.a. Krazy by Dr. Harry Coover, •Cellophane,, was developed in 1908 by Swiss chemist Jacques Brandenberger, •Rayon, the first synthetic silk, by French chemist Hilaire de Chardonnet, an assistant to Louis Pasteur. •Aspartame by G.D. Searle, who was trying to develop a test for an anti-ulcer drug. •Viagra an anti-impotence drug. It was initially studied for use in hypertension and angina pectoris. •The first benzodiazepine, chlordiazepoxide (Librium) 1954 by Leo Sternbach


Organic Chemistry

• Perkin (1856)

– Wanted Quinine

– Made Mauveine

William Henry Perkin (1838-1907)

Quinine was extracted from cinchonatree, discovered by the QuechuaIndians of Peru, and brought to Europe by the Jesuits.

Perkin was 18 years old when he made the first synthetic dye. Later it was produced industrially

5


Organic Chemistry

• 1874 - Othmer Zeidler

• DDT

1939 - insecticidal properties discovered1948 Nobel Prize for Paul Hermann Müller1962, Silent Spring

1972, DDT being banned in the US


Understanding molecular structureFriedrich August KekuleArchibald Scott Couper1858 – tetravalent carbon

LewisPauling

Pople

6


Organic Chemistry

• In the XX Century

– Structure elucidation

– Chemical synthesis

– Petrochemistry

– Pharmaceuticals

– Cosmetics

– Polymers

– Molecular electronics

– Ecological problems

– Adverse use of substances

– Chemical warefare

Robert Burns Woodward (1917 – 1979)


Molecules That Changed the World

• Aspirin®

• Camphor

• Terpineol

• Tropinone

• Haemin

• Quinine

• Morphine

• Steroids & the Pill

• Strychnine

• Penicillin

• Longifolene

• Postaglandins & Leukotrienes

• Vitamin B12

• Erythronolide B & Erythromycin A

• Avermectin

• Amphotericin B

• Glinkgolide B

• Palytoxin

• Taxol®

• Mevacor®, Brevetoxin B

• Ecteinascidin 743

• Epothilones

• Resiniferatoxin

• Vancomycin

• Thiostrepton

Molecules That Changed the World by K. C. Nicolaou and T. Montagnon

7


Aspirin


Vitamin C

Albert Szent-Györgyi, 1937 Nobel Prize in Medicine for the discovery of vitamin C

30Grapefruit

50Orange

60Strawberry

70Lychee

90Broccoli

90Kiwifruit

130Parsley

190Red pepper

1600Acerola

2000Rose hip

2800Camu Camu

3100Kakadu plum

Amount

(mg / 100g)Plant source Plant synthsis pathway

8


Vitamin C – industrial synthesis

production of synthesized vitamin C is currently estimated at 110,000 tones/year

antioxidant and enzyme cofactor

Humans lost the ability to make vitamin C and need to take it up from dietary sources


Natural or synthetic?

• What is the diference?

• Why synthesis?– Price and availability

– New products

• What is required– Starting materials

– Know how• Molecular structure

• Reactivity

• Characterization

• ...

9


Chemistry (review)

• Atomic structure

• Chemical bonding

• Structure and properties of substances


Organic Chemistry, 6th EditionL. G. Wade, Jr.

Jo BlackburnRichland College, Dallas, TX

Dallas County Community College District 2006, Prentice Hall

10


Atomic Structure

• Atoms: protons, neutrons, and electrons.

• The number of protons determines the identity of the element.

• Some atoms of the same element have a different number of neutrons. These are called isotopes.

• Example: 12C, 13C, and 14C=>


Electronic Structure

• Electrons: outside the nucleus, in orbitals.

• Electrons have wave properties.

• Electron density is the probability of finding the electron in a particular part of an orbital.

• Orbitals are grouped into “shells,” at different distances from the nucleus.

=>

11


First Electron Shell

The 1s orbital holds two electrons.


Second Electron Shell

2s orbital (spherical) =>

Three p orbitals

2p orbital

12


Electronic Configurations

• Aufbau principle: Place electrons in lowest energy orbital first.

• Hund’s rule: Equal energy orbitals are half-filled, then filled.

• 6C: 1s2 2s2 2p2

↑↓

↑↓

↑

=>

↑


Electronic Configurations

=>

13


Bond Formation

• Ionic bonding: electrons are transferred.

• Covalent bonding: electron pair is shared.

=>


Lewis Structures

• Bonding electrons

• Nonbonding electrons or lone pairs

Satisfy the octet rule! =>

C

H

H

H

OH

14


Multiple Bonding

=>


Dipole Moment

• Amount of electrical charge x bond length.

• Charge separation shown by electrostatic potential map (EPM).

• Red indicates a partially negative region and blue indicates a partially positive region.

=>

15


Electronegativity and Bond Polarity

Greater ∆EN means greater polarity

=>


Calculating Formal Charge• For each atom in a valid Lewis structure:

• Count the number of valence electrons

• Subtract all its nonbonding electrons

• Subtract half of its bonding electrons

C

H

H

H

C

O

O P

O

OO

O

3-

=>

16


Ionic Structures

C

H

H

H N

H

H

H

+

Cl-

Na O CH3 or O CH3Na+

_

X

=>


Resonance

• Only electrons can be moved (usually lone pairs or pi electrons).

• Nuclei positions and bond angles remain the same.

• The number of unpaired electrons remains the same.

• Resonance causes a delocalization of electrical charge.

Example=>

17


Resonance Example

• The real structure is a resonance hybrid.• All the bond lengths are the same.• Each oxygen has a -1/3 electrical charge.

=>

N

O

OO

_ _

N

O

OO

_

N

O

OO


Major Resonance Form• has as many octets as possible.

• has as many bonds as possible.

• has the negative charge on the most electronegative atom.

• has as little charge separation as possible.

Example=>

18


Resonance Hybrid

majorcontributor

minor contributor, carbon does

not have octet=>


Chemical Formulas

• Full structural formula (no lone pairs shown)

• Line-angle formula

• Condensed structural formula

• Molecular formula

• Empirical formula

• CH3COOH

• C2H4O2

• CH2O =>

C

H

H

H

C

O

O H

19


Calculating Empirical Formulas

• Given % composition for each element, assume 100 grams.

• Convert the grams of each element to moles.

• Divide by the smallest moles to get ratio.

• Molecular formula may be a multiple of the empirical formula.

=>


Sample Problem• An unknown compound has the

following composition: 40.0% C, 6.67% H, and 53.3% O. Find the empirical formula.

molCmolCgC

gC33.3

/0.12

0.40=

molHmolHgC

gH60.6

/01.1

67.6=

molOmolOgO

gO33.3

/0.16

5.53=

3.33

3.33

3.33

= 1

= 1

= 1.98 = 2

CH2O

20


Arrhenius Acids and Bases

• Acids dissociate in water to give H3O+ ions.

• Bases dissociate in water to give OH- ions.

• Kw = [H3O+ ][OH- ] = 1.0 x 10-14 at 24°C

• pH = -log [H3O+ ]

• Strong acids and bases are 100% dissociated.

=>

1 M1 M

Cl-

+H3O+

H2O+HCl


BrØnsted-Lowry Acids and Bases

• Acids can donate a proton.

• Bases can accept a proton.

• Conjugate acid-base pairs.

CH3 C

O

OH + CH3 NH2 CH3 C

O

O-

+ CH3 NH3+

acid conjugatebase

base conjugateacid

=>

21


Acid and Base Strength

• Acid dissociation constant, Ka

• Base dissociation constant, Kb

• For conjugate pairs, (Ka)(Kb) = Kw

• Spontaneous acid-base reactions proceed from stronger to weaker.

CH3 C

O

OH + CH3 NH2 CH3 C

O

O-

+ CH3 NH3+

pKa 4.74 pKb 3.36 pKb 9.26 pKa 10.64

=>


Structural Effects on Acidity

• Electronegativity

• Size

• Resonance stabilization of conjugate base

=>

22


Electronegativity

As the bond to H becomes more polarized, H becomes more positive and the bond is easier to break.

=>


Size

• As size increases, the H is more loosely held and the bond is easier to break.

• A larger size also stabilizes the anion.

=>

23


Resonance

• Delocalization of the negative charge on the conjugate base will stabilize the anion, so the substance is a stronger acid.

• More resonance structures usually mean greater stabilization.

CH3CH2OH < CH3C

O

OH < CH3 S

O

O

OH

=>


Lewis Acids and Bases

• Acids accept electron pairs = electrophile

• Bases donate electron pairs = nucleophile

=>

24


Wave Properties of Electrons

• Standing wave vibrates in fixed location.

• Wave function, ψ, mathematical description of size, shape, orientation.

• Amplitude may be positive or negative.

• Node: amplitude is zero.

=>


Wave Interactions

• Linear combination of atomic orbitals– on different atoms produce molecular

orbitals

– on the same atom give hybrid orbitals.

• Conservation of orbitals.

• Waves that are in phase add together.Amplitude increases.

• Waves that are out of phase cancel out. =>

25


Bonding Region

• Electrons are close to both nuclei.

=>


Sigma Bonding

• Electron density lies between the nuclei.

• A bond may be formed by s-s, p-p, s-p, or hybridized orbital overlaps.

• The bonding MO is lower in energy than the original atomic orbitals.

• The antibonding MO is higher in energy than the atomic orbitals.

=>

26


Bonding Molecular Orbital

Two hydrogens, 1s constructive overlap

=>


Anti-Bonding Molecular Orbital

Two hydrogens, destructive overlap.

=>

27


H2: s-s overlap

=>


Cl2: p-p overlap

=>

Constructive overlap along the sameaxis forms a sigma bond.

28


HCl: s-p overlap

Question: What is the predicted shape for the bonding MO and the antibonding MO of the HCl molecule?

=>


Pi Bonding• Pi bonds form after sigma bonds.

• Sideways overlap of parallel p orbitals.

=>

29


Multiple Bonds

• A double bond (2 pairs of shared electrons) consists of a sigma bond and a pi bond.

• A triple bond (3 pairs of shared electrons) consists of a sigma bond and two pi bonds.

=>


Molecular Shapes

• Bond angles cannot be explained with simple s and p orbitals. Use VSEPR theory.

• Hybridized orbitals are lower in energy because electron pairs are farther apart.

• Hybridization is LCAO within one atom, just prior to bonding.

=>

30


sp Hybrid Orbitals

• 2 VSEPR pairs

• Linear electron pair geometry

• 180° bond angle

=>


sp2 Hybrid Orbitals• 3 VSEPR pairs

• Trigonal planar e- pair geometry

• 120°bond angle

=>

31


sp3 Hybrid Orbitals

• 4 VSEPR pairs

• Tetrahedral e- pair geometry

• 109.5°bond angle

=>


Sample Problems• Predict the hybridization, geometry,

and bond angle for each atom in the following molecules:

• Caution! You must start with a good Lewis structure!

• NH2NH2

• CH3-C≡C-CHO

CH3 C

O

CH2

_

=>

32

w3.ualg.pt\~abrigas QOI 0809 A1 63=>

• Single bonds freely rotate.

• Double bonds cannot rotate unless the bond is broken.

Rotation around Bonds


Isomerism

• Same molecular formula, but different arrangement of atoms: isomers.

• Constitutional (or structural) isomers differ in their bonding sequence.

• Stereoisomers differ only in the arrangement of the atoms in space. =>

33


Structural Isomers

CH3 O CH3 and CH3 CH2 OH

CH3

CH3

and

=>


Stereoisomers

C C

Br

CH3

Br

H3C

C C

CH3

Br

Br

H3C

and

Cis - same side Trans - across

Cis-trans isomers are also called geometric isomers.There must be two different groups on the sp2 carbon.

C CH3C

H H

HNo cis-trans isomers possible

=>

34


Bond Dipole Moments

• are due to differences in electronegativity.

• depend on the amount of charge and distance of separation.

• In debyes,

µ = 4.8 x δ (electron charge) x d(angstroms)

=>


Molecular Dipole Moments

• Depend on bond polarity and bond angles.

• Vector sum of the bond dipole moments.

=>

35


Effect of Lone Pairs

Lone pairs of electrons contribute to the dipole moment.

=>


Intermolecular Forces

• Strength of attractions between molecules influence m.p., b.p., and solubility, esp. for solids and liquids.

• Classification depends on structure.

– Dipole-dipole interactions

– London dispersions

– Hydrogen bonding=>

36


Dipole-Dipole Forces

• Between polar molecules.

• Positive end of one molecule aligns with negative end of another molecule.

• Lower energy than repulsions, so net force is attractive.

• Larger dipoles cause higher boiling points and higher heats of vaporization.

=>


Dipole-Dipole

=>

37


London Dispersions

• Between nonpolar molecules

• Temporary dipole-dipole interactions

• Larger atoms are more polarizable.

• Branching lowers b.p. because of decreased surface contact between molecules.

=>


Dispersions

=>

38


Hydrogen Bonding

• Strong dipole-dipole attraction.

• Organic molecule must have N-H or O-H.

• The hydrogen from one molecule is strongly attracted to a lone pair of electrons on the other molecule.

• O-H more polar than N-H, so stronger hydrogen bonding. =>


H Bonds

=>

39


Boiling Points and Intermolecular Forces

CH3 CH2 OH

ethanol, b.p. = 78°C

CH3 O CH3

dimethyl ether, b.p. = -25°C

trimethylamine, b.p. 3.5°C

N CH3H3C

CH3

propylamine, b.p. 49°C

CH3CH2CH2 N

H

H

ethylmethylamine, b.p. 37°C

N CH3CH3CH2

H

CH3 CH2 OH CH3 CH2 NH2

ethanol, b.p. = 78°C ethyl amine, b.p. = 17 °C


Solubility

• Like dissolves like.

• Polar solutes dissolve in polar solvents.

• Nonpolar solutes dissolve in nonpolar solvents.

• Molecules with similar intermolecular forces will mix freely.

=>

40


Ionic Solute with Polar Solvent

Hydration releases energy.Entropy increases.

=>


Ionic Solute withNonpolar Solvent

=>

41


Nonpolar Solute withNonpolar Solvent

=>


Nonpolar Solute with Polar Solvent

=>

42


Classes of Compounds

• Classification based on functional group.

• Three broad classes

– Hydrocarbons

– Compounds containing oxygen

– Compounds containing nitrogen.

=>


Hydrocarbons

• Alkane: single bonds, sp3 carbons

• Cycloalkane: carbons form a ring

• Alkene: double bond, sp2 carbons

• Cycloalkene: double bond in ring

• Alkyne: triple bond, sp carbons

• Aromatic: contains a benzene ring =>

43


Compounds Containing Oxygen

• Alcohol: R-OH

• Ether: R-O-R'

• Aldehyde: RCHO

• Ketone: RCOR'

CH3CH2 C

O

H

CH3 C

O

CH3

=>


Carboxylic Acids and Their Derivatives

• Carboxylic Acid: RCOOH

• Acid Chloride: RCOCl

• Ester: RCOOR'

• Amide: RCONH2

C

O

OH

C

O

Cl

C

O

O CH3C

O

NH2

=>

44


Compounds Containing Nitrogen

• Amines: RNH2, RNHR', or R3N

• Amides: RCONH2, RCONHR, RCONR2

• Nitrile: RCN

N

O

CH3

CH3 C N

=>


Sources and Resources

• Sources – Organic Chemistry, 6e by L.G. Wade, Jr.

• Resources:– Initial chapter(s) of any good organic chemistry book– links

• http://www.mdli.com/products/framework/chemscape/• http://www.educypedia.be/computer/computerchemistry.htm• http://www.acdlabs.com/• http://www.cambridgesoft.com/• http://www.ux1.eiu.edu/~cfthb/links/model_anim/

– Classes online• http://www.chem.uic.edu/web1/OCOL-II/WIN/STRUCT.HTM• http://www.chem.ucalgary.ca/courses/351/Carey5th/Carey.html• http://www.cem.msu.edu/~reusch/VirtualText/intro1.htm

química orgânica i - ualgw3.ualg.pt/~abrigas/qoi0809a1.pdf · 1 w3.ualg.pt\~abrigas qoi 0809 a1 1...

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