DRAWING ORGANIC STRUCTURESFUNCTIONAL GROUPSCONSTITUTIONAL ISOMERS

Dr. Sheppard

CHEM 2411

Spring 2015

Klein (2nd ed.) sections 2.1 – 2.6, 4.3

Draw Lewis structures…

• C2H6

• CH4O

• C3H6 (contains C=C)

• C4H10 (multiple possible answers)

More Lewis structures…

• CH5N

• CHN

• HNO3

• Remember…• Keep in mind total available valence electrons• Try to minimize formal charges• Patterns for formal charge

Molecular Representations

• Example: isopropyl alcohol (C3H80)

• Lewis structure• Show all bonds, atoms, lone pairs

• Partially condensed/Condensed structure• Omit some bonds (C─C, C─H, O─H, N─H)• Often omit lone pairs• Not the same as a molecular formula

• Skeletal structure/Bond-line structure/Line-angle drawing• Show bond framework as lines• C atoms at intersections of lines (bonds) and end of each line• H atoms bonded to C are not shown• Heteroatoms (atoms other than C and H) are shown

Drawing line-angle structuresName Lewis structure Condensed structure Line-angle drawing

Acetone

Butane

1-Butene

Cyclohexane

Benzene

C C C

O H

H

H

H

H

H

C C C CH

H

H

H

H

H

H

H

H

H

C C C CH

H H H

H

H

H

H

C

C

C

C

C

C

HH

H

H

H

H

H

H

H H

H

H

H H

H

HH

H

Lone Pairs on Line-angle Drawings• Formal charges must be shown• Lone pairs may be omitted, and can be determined from

structure

Lone Pairs on Line-angle Drawings

Interpreting Line-angle Structures• What is the molecular formula for the following:

• What is the molecular formula for adrenaline?

• What is the molecular formula for thalidomide?

HO

OH

N

HO

H

N

N

O

O O

O

H

Molecular Representations• Which Lewis structure is correct?

H C

H

H

O C H

O

H C

H

H

O C H

O

H C

H

H

O C H

O

H C

H

H

O C H

O

Molecular Representations• Draw partially condensed and line-angle structures for this

condensed structure: (CH3)3CCH2COCHCH2

• How many hydrogens on each carbon atom?

3D Organic Structures• Remember, carbons are tetrahedral

• Use dashes and wedges to show 3D structure

C Cis really

Br HBr

is or

BrH

Functional Groups• Collection of atoms at a site within a molecule with a

common bonding pattern• Reacts in a typical way, generally independent of the rest of

the molecule

• Four broad classes• Hydrocarbons• Compounds containing O• Compounds containing N• Compounds containing S or P

1. 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 (arene): contains a benzene ring

• Not a hydrocarbon, but related…

• Alkyl halide: R─X • R = any carbon group

• X = halogen

2. Compounds containing oxygen• Alcohol: R─OH• Ether: R─O─R'• Carbonyl group: C=O

• 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' (RCO2R’)

• Amide: RCONH2

• Acid Anhydride: RCO2COR

C

O

OH

C

O

Cl

C

O

OCH3

C

O

NH2

C

O

C

O O

3. Compounds containing nitrogen

• Amines: RNH2, RNHR', or R3N

• Amides: RCONH2, RCONHR, RCONR2

• Nitrile: RCN CH3 C N

4. Compounds containing S or P

• Phosphates (PO42-)

• Thiol (R─SH)

• Sulfides (R─S─R)

• Sulfoxides (S=O)

• Thioester (RCOSR)

Functional Groups• Identify the functional group(s) present in the following

molecules.

OH

NH

O

OH

O

O

O

O

OH

NH2

(a)

(b)

(c)

(d)

(e)

(f)

(g)

Functional Groups• Identify the functional groups present in thalidomide:

• Draw as many structures as you can with the molecular formula C4H8O2. Identify the functional groups present in each structure.

N

N

O

O O

O

H

Isomers• Isomers have the same molecular formula, but different

arrangements of atoms

• Constitutional isomers • differ in their connectivity

• Stereoisomers• differ in the spatial arrangement/orientation of their atoms

Constitutional Isomers• Molecules with the same molecular formula, but different

connectivity• Same number and kinds of atoms• Differ in which atoms are bonded

• Example: C4H10

• Straight-chain (“normal”) alkane vs. branched-chain alkane

CH3 CH2 CH2 CH3 CH3 CH CH3

CH3

butane isobutane

Constitutional Isomers

Constitutional Isomers• Are the following pairs of molecules constitutional

isomers, the same molecule, or neither?

(a)

(b)

(c)

(d)

CH3 CH2 CH CH3

CH2 CH3

CH3 CH2 CH CH2 CH3

CH3

CH CH2 CH2 CH CH2

CH3

CH2

CH3 CH3CH3CH3

CH3

CH3 C

CH3

CH3

CH2 CH3 CH3 C

CH3

CH2

CH2 CH3

CH3

CH3 CH2 CH2 CH2 CH2 CH3 CH2 CH CH2

CH3 CH3 CH3