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Structural Formulas for Organic Molecules

Condensed Skeletal-line

Lewis (Expanded)

Hydrocarbons Part 1: Structural Formulas

Neutral Bonding Patterns for Organic Compounds

C C CH 3 CH 2 CH 2 CH 2 CH (^3)

H H

H H H

C C

H H

C

H H

H

H H

Condensed Structures Because the carbon atoms form the backbone of the skeleton, it is also common to omit the bonds and only show the atoms. Double and triple bonds are often still shown.

The following three structures ALL represent the same compound:

Write the condensed structures for the 5 structural isomers of C 6 H 14.

OH

C

H C N

C

H

H H

H

H

H

Here are “4 different ways” to describe an organic compound:

Molecular Formula vs Lewis Structure vs Bond-Line vs Condensed

Draw these compounds the “other 3 ways” & add the lone pair electrons.

(CH 3 ) 2 CHCH 2 CHO

Conformers

Perspective Formulas, Sawhorses, and Newman Projections 3 different ways to show conformations

Converting the perspective formula for 2,3-dibromobutane into a Newman Projection along the C2-C3 axis.

A (^) B C

Draw the Newman projection for CH 3 CH(CH 3 )CH(CH 3 )CH 2 CH 3 along the C2-C3 axis.

What are the relationships between compounds A, B and C?

trans-2-butene (^) cis-2-butene mp -139C & bp -4C (^) mp -106C & bp 1C

H 3 C CH 3 H 3 C CH 3

trans-1,3-dimethylcyclohexane (^) cis-1,3-dimethylcyclohexane

Geometric Isomers: compounds with the same connectivity between atoms, yet different spatial arrangements.

Cis & trans isomers can NOT inter-convert. They are unique cpds.

Cis-trans Isomers in Biochemistry Isomerization reaction: a chemical reaction that converts one structural isomer or geometric isomer into another The retina of the eye contains 2 types of photoreceptors: rods and cones. The rods contain a polyene known as retinal which is part of a larger protein known as rhodopsin. Light induces one of the cis- double bonds to undergo isomerization reaction to a trans double bond causing the entire molecule to change shape which initiates a nerve impulse that travels along the optic nerve to the brain resulting in a visual image.

1. a) What are the relationships between Cpd I and other Cpds II to VII – identical (I), structural isomers (SI), or geometric isomers (GI)? b) Label all geometric isomers as cis or trans.
2. Use the following compounds to answer the questions below.

A B C D E

a) Which compounds are structural isomers?

b) Which compounds are conformers?

3. Label the following double bonds as cis or trans if applicable.

Root Names – the Homologous Series

C’s Alkane Structure Suffix name Substituent name

1 methane methyl

2 ethane ethyl

3 propane propyl

4 butane butyl

5 pentane pentyl

6 hexane hexyl

7 heptane heptyl

8 octane octyl

9 nonane nonyl

10 decane decyl

-CH 2 -

-CH 2 CH 2 -

-CH 2 CH 2 CH 2 -

Guidelines for Naming Straight-Chain Hydrocarbons and Cycloalkanes

Rule 1: Assign the root by counting the carbon atoms in the chain.

Rule 2: Assign the suffix. Rule 3: Assign a locator number to the root if a multiple-bond is present. The multiple-bond is ALWAYS assigned the lowest possible number. Rule 4: For cycloalkanes and alkenes, assign the cis or trans prefix if applicable.

Draw the skeletal-line structure for each of the following compounds.

a) trans-2-hexene

b) 3-octyne

c) cyclopentane

Give the IUPAC name for the following compounds.

a)

b)

c)

Draw the skeletal-line structure for each of the following compounds.

a) cis-4-ethyl-2-hexene

b) trans-1-ethyl-3-methylcyclohexane

Give the IUPAC name for the following compounds.

a)

b)

c)

OH

Guidelines for Naming Substituted Benzenes

Rule 1: Assign the root name.

Rule 2: Name each substituent.

Rule 3: If there is more than one substituent present, then we number the benzene ring to give the 2nd^ substituent the lowest possible number. The first substituent is always given the number 1.

Rule 4: Assemble the prefix name by listing the substituents in alphabetical order. Place the locator number in front of each substituent name separated by a hyphen. If a substituent is repeated more than once along a chain, then insert an additional prefix di- (2), tri- (3), or tetra- (4) in front.

Memorize the following common benzene derivatives.

Draw the skeletal-line structure for 3-propylphenol.

Give the IUPAC name for C 6 H 5 CH 2 CH 2 CH 2 CH 3.

Complete the table.

IUPAC Name

Skeletal-line Structure

Condensed Structure

4-ethyl-2-methyloctane

CH 3

CH 3 CH 2 CH 2 CH(CH 3 )CH 3

cis-6-ethyl-7-methyl- 3-octene

CH 2 =C(CH 3 )CH 2 CH 3