Chem1 notes L1-6 2018 PDF

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CHEMISTRY 1 Lectures 1-6 Lecture Slides 2018 Professor Mark A. Rizzacasa School of Chemistry [email protected]

CHEM10003-CHEMISTRY 1 Organic Chemistry 6 Lectures-weeks 1-2 Professor Mark Rizzacasa email: [email protected] http://rizzacasa.chemistry.unimelb.edu.au/ Lectures: ! Monday 10 am (Kathleen Fitzpatrick), 2:15 pm (MSD) ! !

Wednesday: 10 am (Kathleen Fitzpatrick), 2:15 pm (MSD) Friday: 10 am (Kathleen Fitzpatrick), 2:15 pm (MSD)

ORGANIC CHEMISTRY Lectures 1-6 Lecture Slides and Overheads 2018 Available on LMS http://www.lms.unimelb.edu.au/ !

Text: Chemistry3 2nd Ed. By Burrows, Holman, Parsons, Pilling & Price Also Organic Chemistry by J McMurry 8th Ed.

CHEM10003 Workbook

Chemistry 1 Facebook group https://www.facebook.com/groups/2018CHEM10003/

For information, asking questions, study help and tools, resources, career information, events… Get to know your classmates and ask them for help.

Bonding in Organic Molecules: The Periodic Table

Bonding in Organic Molecules: The Covalent Bond Hydrogen Atom Atomic number: 1 Atomic weight: 1.01

Hydrogen Ground State Electronic Configuration 1s1

E 1s 1 proton

+

-

-

electron

+

proton

1s orbital

Bonding in Organic Molecules: The Covalent Bond Participating Elements share a pair of electrons

H

H

1s Atomic Orbital

H H Overlap Atomic Orbitals H valence shell filled i.e. 2 electrons

1s Atomic Orbital

Circular cross section H

H

=

H or H H Covalent Bond

H

Molecular Orbital σ-Bond

The H2 Molecule:! H H Potential energy diagram 600

H

400

H

Energy (kJ/mol)

200

H

0 0.5

-200

-400

1

1.5

H 0.74 Å H2 bond length

-600

2

436 kJ/mol H2 bond energy

2.5

3

Internuclear Distance (Å)

H

3.5

Bonding in Organic Molecules:! The Carbon Atom Carbon Atom Atomic number: 6 Atomic weight: 12.01

Carbon Ground State Electronic Configuration 1s2 2s2 2p2 x E

z

y

2p 2s

6 protons & 6 neutrons

-

1s

-

+ ++++

-

-

electron

+

proton neutron

-

1s orbital 2s orbital

Carbon atom

2p orbital

Bonding in Organic Molecules:! Hybridisation: The Structure of Methane CH4 Carbon forms 4 covalent bonds: 4 orbitals with one electron in each required However, all bonds in CH4 are the same Carbon Ground State Electronic Configuration

x E

y

z

2p

~400 kJ/mol

E

2p

2s

2s

1s

1s

Combine 1 x s + 3 x p

Hybridise

E

2 sp3

4 new x

sp3

hybrid orbitals

1s

sp3

sp3

sp3

Bonding in Organic Molecules:! Hybridisation: The Structure of Methane CH4 2nd shell

s

electron (e–) + + + px pz Atomic orbitals py +

+

sp3 sp3 Hybrid orbitals

Hybridise

+ sp3

sp3

Bonding in Organic Molecules:! Hybridisation: The Structure of Methane CH4 sp3 hybridized carbon TETRAHEDRAL

s - sp3 overlap

H

C

+ 4x H C H

Circular cross section

H

H

σ-C–H bond

H

Carbon valence shell filled (8 electrons)

Bond behind page

C H H Bond in plane of page

H Bond out of page

4 electron pairs as far apart as possible around C atom Valence Shell Electron Pair Repulsion Theory (VSEPR)

Bonding in Organic Molecules:! Hybridisation: The Structure of Methane CH4

H

sp3 hybridised

C H

H H

Tetrahedral

m.p. –182°C b.p. –160°C

Methane lake on Titan (Moon of Saturn)

Ball and Stick Model

Space Filling Model

H

H

C

H H

Van der Waals Radii C atom ~ 1.7 Å

H atom ~1.2 Å

Bonding in Organic Molecules:! The Structure of Ethane C2H6 2 x sp3 hybridized carbon atomsTETRAHEDRAL

sp3 - sp3 end-on-end overlap

H C

H H

C

H H

H

σ-C–C H bond C

H H C

H H

Ethane C2H6 H

H

H C

C

H H

H

H σ-C–H bond

Alkanes (Hydrocarbons) CnH2n+2

Propane C3H8

Butane C4H10

Unusual Names for Hydrocarbons

Paddlane

Snoutene

Birdcage

Cubane

George

Pagodane Bi-George

Barstardane

Alkanes ! (Saturated Hydrocarbons) •  Methane CH4 CnH2n+2 •  •  •  •  •  •  •  •  • 

Ethane Propane Butane Pentane Hexane Heptane Octane Nonane Decane

C2H6 C3H8 C4H10 C5H12 C6H14 C7H16 C8H18 C9H20 C10H22

NOMENCLATURE! IUPAC rules! International! Union of! Pure and! Applied! Chemistry

Number of carbons

Prefix–Parent–Suffix The substituents

The family (Alkanes = ane)

ALKANE NOMENCLATURE 1) Name the longest linear carbon chain (with the most substituents if there are two the same). !  2) Number the atoms in the main chain from the end nearest the first branch point. !  3) Name the substituents in alphabetical order using numbers to locate on carbon chain (Locants separated by hyphen) !  4) Name the substituents. ! 

ALKANE SUBSTITUENTS •  •  •  •  •  •  •  • 

Methyl Ethyl Propyl Isopropyl tert-Butyl

–CH3 –CH2CH3 –CH2CH2CH3 –CH (CH3)2 –C (CH3)3 x2 Di x3 Tri x4 Tetra

C6H14: 5 Structural Isomers Shorthand Structure H3C

CH2 CH2

1

2

H3C

3

CH2

1

2

CH2

4

CH

CH2

3

4

Skeletal Structure

CH2

5

CH3

6

Hexane

CH3

5

CH3

3-Methylpentane CH3

H3C

CH2 CH2

5

4

CH

2

3

CH3

1

CH3 H3C

CH2

4

C

2

3

CH3

1

CH3

1

2,2-Dimethylbutane 4

CH3

H3C CH H3C

2-Methylpentane

2

CH

3

CH3

2,3-Dimethylbutane

Alkanes: Nomenclature examples Shorthand Structure

(1)

H2C

CH2

CH3

H3C C

CH2

CH3

Skeletal Structure

CH3

H2C CH3 (2)

H2C

CH CH2 CH3

H3C C CH2 CH2 CH3 CH3

H3C CH2 CH2 (3)

H3C

H3C CH2 CH CH2

CH CH

CH3 CH2 CH3

Alkanes: Sources and Uses The main source of alkanes is petroleum Boiling range

Number of Carbon Atoms Use

Below 20°C

C1-C4

Natural gas, petrochemicals, plastics

20-100°C

C5-C7

Solvents

20-200°C

C5-C12

Petrol

200-300°C

C12-C18

Kerosene, jet fuel

200-400

C12 and higher

Heating oil, diesel

Octane b.p. 126°C

2-Methylheptane b.p.118°C

2,2,4-Trimethylpentane b.p. 99°C

Cubane m.p. 130-131°C

Haloalkanes! (Alkyl halides) Halogens F, Cl, Br, I Each can form one covalent bond to carbon (7 valence electrons) Lone pairs Nomenclature prefix (Valence electrons H not involved in bonding) F = Fluoro H Cl = Chloro F H Br = Bromo Fluoromethane (C–F Bond length 1.39 Å, Bond strength 460 kJ/mol) I = Iodo

H H H

I

Iodomethane (C–I Bond length 2.14 Å, Bond strength 239 kJ/mol) Cl

Br

1

Cl

F F

Dichlorodifluoromethane (Freon-12 banned due to ozone depletion)

3

2

1

7

4 5

Cl

Br

1-Bromo-3-chloropropane

5-Bromo-2,4-dimethylheptane

Conformational Isomers! ETHANE"

H H

H

C

C

H

H

H

Conformations of Ethane! Energy Diagram" Eclipsed! HH

HH

H H

HH

HH

H H

HH

HH

Energy

H H

12 kJ/mol!

H

H

H

H

H

H

H

H

180

H

H

Staggered!

H

H H

H

120

60

H

H

H

0

H

60

H

H

H H

H

Dihedral Angle °

H

120

180

The Conformational Isomers (conformers) of ETHANE

H

H

H

H

H

H

Newman projections H

HH

H

Front Carbon

H

θ = 60° H

60°

H H

θ = dihedral angle

H

Front Carbon

H

60°

H

H H H

HH

H H

Conformational Isomers! BUTANE"

H H

CH3

C

C

H3C

H

H

Conformations of Butane! Energy Diagram" Eclipsed!

H H

H H

H3CCH

3

HH

HCH3

H CH3

HCH 3

H CH

3

Energy

Gauche! H

16 kJ/mol!

H

H H3C

Gauche!

H

19 kJ/mol!

H

H H

16 kJ/mol!

3.8 kJ/mol!

CH3 H

H

H H H3C Anti!

180

H

H3C H3C

CH3

3.8 kJ/mol! H

H H

H Anti! H3C

Staggered! 120

60

0

Dihedral Angle °

CH3

60

120

H H

180

The Conformational Isomers (conformers) of BUTANE

4 H3C

H

H

3

Look down C2-C3 bond

2 H

1CH3

H

Newman projections

θ = 60° CH3

CH3 H

Front Carbon

H

H3C

H

θ = 180° H

120°

H

H

H

CH3

H

Front Carbon

H

CH3 θ = 60° CH3

H

120°

H H

H3CH

HH

H3CCH

CH H 3

HH

3

H H

1969 Nobel Prize in Chemistry"

Sir Derek Barton(1918-1998)"

Odd Hassel" (1897-1981)"

“for their contributions to the development of the concept of conformation and its application in chemistry”"

Chiral objects have a nonsuperimposable mirror image!

Left hand! Non-chiral!

Chiral!

H C I

Right hand!

Chiral molecules! Cl Br Tetrahedral carbon atom (sp3)! with 4 different substituents is! an asymmetric carbon atom!

Chiral molecules!

Mirror Plane!

Mirror Image!

NON-SUPERIMPOSABLE Mirror images!

NON-SUPERIMPOSABLE Mirror images!

Alanine (amino acid)! L-Alanine

D-Alanine

H C H3C

H NH2 CO2H

S-Natural isomer [α]D +8.5

H2N C HO2C

CH3

R-Unnatural isomer [α]D –8.5 mirror plane

Enantiomers: Stereoisomers that have identical physical and chemical characteristics EXCEPT in their behaviour towards plane polarised light and their reactivity in a CHIRAL environment!

Polarimeter! Chiral molecules can rotate plane polarised light!

Specific rotation [α]D = !

α! lxc!

Enantiomers! Enantiomers often behave differently in a chiral environment!

The Significance of Chirality! Carvone enantiomers

O

O

(S)-Carvone Caraway seeds

(R)-Carvone Spearmint

The Significance of Chirality! Thalidomide enantiomers

O

O O

N NH O

O

(S)-Thalidomide Teratogenic!!! (causes birth defects)

O

N HN O

O

(R)-Thalidomide Treatment for morning sickness

ASSIGNING THE ABSOLUTE CONFIGURATION ABOUT AN ASYMMETRIC CARBON ATOM!

Cahn-Ingold-Prelog (CIP) Rules! •  RULE 1: DETERMINE THE PRIORITY of the four substituents attached to the asymmetric centre by listing them in order (1,2,3,4) of decreasing ATOMIC NUMBER of the atoms attached directly to the asymmetric carbon.! •  RULE 2: VIEW the molecule along the bond from the asymmetric carbon atom to the LOWEST priority atom then look at the order (1→2→3)!

2 Br

2-Br 4-H

H4

Cl 3

3-Cl

R I 1

1-I

IF CLOCKWISE THEN DENOTED AS R 3 Cl

H4

Br 2

3-Cl 4-H

S I 1

IF ANTICLOCKWISE THEN DENOTED AS S

1-I

2-Br

Stereoisomers: Examples

OH

CH3 H C OH H3CH2C

and

H C CH2CH3 H3C

Br H H3C

CH3

H3C H and

H Br

H3C H Br

HO H HO H

H OH H OH OH

OHC HO

H

Br

and

HO

CHO H OH

Cycloalkanes 60°

H2 C

120° IF FLAT

= H2C

CH2

Smallest C3H6 90°

Cyclohexane Cyclopropane

Angle deviated from sp3 109.5° Ring Strain

C6H12

Cyclobutane Cycloheptane C4H8 C7H14

108°

Cyclopentane C5H10

Cyclooctane C8H16

H H H H

H H

Cyclopropane

Cycloalkanes: Ring Strain Energies 120.0

Relative Strain Energy (KJ/mol)

100.0

80.0

60.0

40.0

20.0

0.0 3

4

5

6

7

8

Ring size

Cyclohexane

9

10

Cyclohexane Ring-Flip H H H H H H HH H H H H

43 KJ/mol

H H H H H H

HH

H H H H

Cyclohexane H H H

H

H

H H H

H

H H

H

H

Chair Conformation

H

H

H H H

H

H H

H H

H

Boat Conformation

Cyclohexane Axial and Equatorial Hydrogens H H H H HH H H H H H H

H HH

H H H

H

H H H

H H

Cyclohexane ring flip energy diagram Half-chair

Half-chair

Twist Boat

Boat

43 kJ/mol

Twist Boat

43 kJ/mol

29 kJ/mol

Chair Conformation

Chair Conformation

Methylcyclohexane

1,3-Diaxial Steric interaction

H

H H

H H

H H

H H H H

H H

CH3

H H

20°C

Equatorial (eq)

H

95.8%

3

H H

CH3 Axial (ax) H1 H 7.6 kJmol H H

4.2%

Preferred conformer

1,3-Diaxial Steric interaction

Tert-Butylcyclohexane H H H

H H

H H H

H3 C CH3 20°C H C CH3 H Equatorial (eq) H 99%

CH3 H3 C Axial (ax) H C CH3 H H H H 22.8 kJ/mol H H H H H H 1%

Preferred conformer 1,3-Diaxial Steric interaction

Cis-trans Isomerism! Disubstituted cyclohexanes !  Unlike

open chain alkanes, C-C bonds in cycloalkanes cannot rotate freely !  This means that groups attached to the ring retain their relative orientation with respect to the plane of the ring !  Groups

on the same face of a ring are called cis

!  Groups

on opposite faces of a ring are called

trans

Cis-trans Isomerism! Disubstituted cyclohexanes CH3

cis = same side of ring plane IF FLATTENED OUT

CH3

CH3 H

CH3

H

BUT CYCLOHEXANE RING IS IN the CHAIR CONFORMATION !

cis-1,3-Dimethylcyclohexane

Chair conformations of cis-1,3-Dimethylcyclohexane 1,3-Diaxial Steric interaction

equatorial axial

CH3 H H H3C axial H H H H H H H H

RING FLIP H H

H H H H3C H H

H CH3

H H

equatorial PREFERRED CONFORMER

Cis-trans Isomerism! Disubstituted cyclohexanes CH3

trans = opposite side of ring plane IF FLATTENED OUT

CH3 H H

CH3

CH3

trans-1,3-Dimethylcyclohexane Chair conformations of trans-1,3-Dimethylcyclohexane

Cis-trans Isomerism Axial (ax) and Equatorial (eq) Relationships in Cis- and TransDisubstituted Cyclohexanes 1,2-Cis

ax,eq or eq,ax

1,2-Trans

ax,ax or eq,eq

1,3-Cis

ax,ax or eq,eq

1,3-Trans

ax,eq or eq,ax

1,4-Cis

ax,eq or eq,ax

1,4-Trans

ax,ax or eq,eq

Cycloalkanes: Nomenclature !  Step

1

!  The

!  Step

Find the parent parent is the largest ring

2

Number the ring

!  For

substituted cycloalkanes, place a substituent at C1. Number the ring so that the second substituent has the lowest possible number

Br

5

4

1

H

H

Example

3 2

CH2CH3

trans- 1-Bromo-3-ethyl cyclopentane 1. Find the parent The parent ring is...