Aromatic Lesson

Aromatics compounds

Mrs Levine

​Objective

• Define Cyclic Hydrocarbons

• Name CyclicHydrocarbons

• Define aromatic compounds.

• Describe Benzene Ring

• Name Benzene rings

In some hydrocarbon compounds, the carbon chain is in the form of a ring. Compounds that contain a hydrocarbon ring are called cyclic hydrocarbons

• Carbons form a ring structure

• General formula (cyclic alkane): CnH2n

• Prefix:  cyclo-

​

​Cyclic Hydrocarbons

​Example: cyclohexane, C₆H₁₂

1. Determine the length of the parent chain (please note this could be a straight chain parent chain or a cyclic parent chain).

2. If the parent chain is cyclic:

   1. Name the alkane with the prefix cyclo-

   2. Name the side chains, giving the lowest combination of number for the carbons they are attached to

​Naming Cyclohydrocarbons

​Example:
Parent chain = hexanecyclohexane
Side chains: 1 methyl & 1 ethyl

​Name: 1-ethyl-3-methylcyclohexane

c. Sometimes the cyclic hydrocarbon can be a side chain of the straight- parent chain.
In this case, we change the ending of the cyclic portion to –yl, to Indicate it is a side chain/branch.

​Naming Cyclohydrocarbons

Multiple Choice

What prefix do we use for alkanes that are arranged in a loop?

• ring-

• cyclic-

• cyclo-

Multiple Choice

What is the IUPAC nomenclature of this structure?

• 1,2,3-trimethylcyclopropane

• 1-methyl-2-methyl-3-methylcyclopropane

• 1,2,3-trimethylcyclopropyl

• 1,2,3-trimethylpropane

Multiple Choice

Structure of 2,4-dibromo-1-fluorocyclohexane is...

Draw

Draw Cyclobutane

Aromatics and Benzene

​

Aromatic

​• Aromatic compounds contain benzene.
• Benzene, C6H6 , is represented as a six carbon ring with 3 double bonds.
• Two possible isomers can be drawn to show benzene in this form.
• Tend to be pleasant smelling, but some are not
• The most common aromatic ring is benzene which includes 6 Carbons and 6 Hydrogens--it is highly unsaturated
• Strangely, aromatics do not undergo the same kinds of reactions as alkenes and alkynes
• The benzene ring is planar and hexagonal
• The three double bonds in benzene are shared equally between the six carbons. We say that the double bonds are delocalized
• Benzene is unusually stable and resists most reactants

Open Ended

Which of the following structures is a benzene? Why?

​What is the difference between these structures?

Multiple Choice

Identify benzene as a saturated or an unsaturated hydrocarbon.

• Saturated

• Unsaturated

Multiple Choice

The chemical formula of the simplest aromatic is: 

• CH₄

• C₂H₂

• C₆H₆

• C₆H₁₂

​Vanilla

Multiple Choice

​Is an artificial sweetener, is commonly used in soft drinks and diet drinks.

• Vanilla

• Aspartame

• Saccharin

• Naphthalene

​Bonding and Resonance Structures for Benzene

​Resonance is a means to represent a molecule that only one Lewis structure does not adequately describe.

The structures for benzene can also be written as a single structure where the alternating double bonds are written as a circle within the ring.

​

​•Benzene Structure

 

Multiple Choice

Which compound below is aromatic?

Multiple Choice

Because they have aromas, compounds with a ring of resonance bonds are called ___

• fragrent compounds

• pungent molecules

• aromatic compounds

• scented structures

Multiple Choice

Cycloalkynes do exist but they are extremely hard to form because the triple bond is ___

• linear

• bent

• tetrahedral

• unbreakable

Multiple Choice

Using the structural diagram, name this compound.

• 1,2-diethylbenzene

• 1,2-dimethylbenzene

• 1,2-diethylcyclohexane

• 1,2-dimethylcyclohexane

​Objectives

• Name simple compounds containing benzene.

• Draw simple compounds containing benzene.

​Naming Benzene Structures

​The simplest aromatic compounds are benzene rings with one substituent replacing one of the hydrogen atoms.

​

The naming is simply the name of the branch plus Benzene.

​Two substituent groups

​If more than one substituent is present, their location relative to each other can be indicated by numbering the positions on the benzene ring.

​The branches are both methyl groups The locations of the methyl groups are on C1 and C2 The name of the molecule is 1,2−dimethylbenzene

• ​When more than one similar substituent group is present in the ring, they are labelled with the Greek numerical prefixes such as di, tri, tetra.

• Substituents are named in alphabetical order

​Drawing Benzene Structures

Multiple Choice

What is the IUPAC name of the following compound?

• 1-bromo-3-fluoronitrobenzene

• 4-bromo-2-fluoronitrobenzene

• 5-bromo-1-fluoronitrobenzene

• 3-bromo-1-fluoronitrobenzene

Draw

Draw 1-methyl, 3-ethylbenzene