Todd:Chem3x11 ToddL2

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(Opening section on cycloalkanes)
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The stereochemistry is ''cis'' because the two methyls are on the same face of the ring (coming towards us). Remember that ''cis'' and ''trans'' isomers can only be interconverted by breaking bonds - they are configurational isomers.  
The stereochemistry is ''cis'' because the two methyls are on the same face of the ring (coming towards us). Remember that ''cis'' and ''trans'' isomers can only be interconverted by breaking bonds - they are configurational isomers.  
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So the full name of this molecule is ''cis''-1,3-dimethylcyclohexane. We write the name left to right, but we devised the name right to left.
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So the full name of this molecule is '''''cis''-1,3-dimethylcyclohexane'''. We write the name left to right, but we devised the name right to left.
==Why Cycloalkanes Aren't Flat==
==Why Cycloalkanes Aren't Flat==

Revision as of 07:00, 13 April 2012

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Contents

Chem3x11 Lecture 1

Coming (Apr 12).

(Back to the main teaching page)

Key concepts

  • Cycloalkanes have 3D structure
  • Cyclohexane has a chair conformation and a less stable boat conformation
  • Dynamic movement of cyclohexane causes "ring-flipping" which swaps axial and equatorial substituents

Cycloalkanes

Basic Types of Cycloalkanes

Cycloalkanes are, as might be expected, cyclic alkanes, with general formula CnH2n, with a logical naming system:

Scheme 1: The Names of Simple Cycloalkanes
Scheme 1: The Names of Simple Cycloalkanes

Naming Substituted Cycloalkanes (revision from Y1)

The nomenclature is like any other organic molecule:

Scheme 2: Basic Naming Convention for Most Organic Molecules
Scheme 2: Basic Naming Convention for Most Organic Molecules

...and you name the molecule right to left. i.e. stem (parent) first, then the subsituents, then the stereochemistry. Let's try one:

Scheme 3: Example Substituted Cycloalkane to Name
Scheme 3: Example Substituted Cycloalkane to Name

The parent ring is cyclohexane. There are two methyl groups hanging off the ring, and we have to specify unambiguously where they are. Take one of them as number "1" and number the other atoms around the ring in order, keeping the numbers as low as possible, i.e.:

Scheme 4: Numbers are Kept Low in Molecule Numbering
Scheme 4: Numbers are Kept Low in Molecule Numbering

The stereochemistry is cis because the two methyls are on the same face of the ring (coming towards us). Remember that cis and trans isomers can only be interconverted by breaking bonds - they are configurational isomers.

So the full name of this molecule is cis-1,3-dimethylcyclohexane. We write the name left to right, but we devised the name right to left.

Why Cycloalkanes Aren't Flat

Despite the freedom to buckle and move, remember that rings have far less conformational freedom than their acyclic counterparts.

The Licence for This Page

Is CC-BY-3.0 meaning you can use whatever you want, provided you cite me.

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