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ODU / Engineering / CHEM 213 / How do you convert cyclohexane to chair conformation?

How do you convert cyclohexane to chair conformation?

How do you convert cyclohexane to chair conformation?

Description

Study Guide for Exam II 


How do you convert cyclohexane to chair conformation?



Topics: 

Stereochemistry

● Converting Dash/Wedge cyclohexane into a chair conformation:

○ If dashed substituents, the substituents should be pointing down in a chair conformation ○ If wedged substituents, the substituents should be pointing up in a chair conformation ● Chirality

○ Two molecules are identical (conformers) if models of the two can be superimposed without  breaking any bonds

○ Mirror images (enantiomers): look like reflections of one another 

■ Ex. change from R configuration to a S configuration

○ Chiral­ not identical to its mirror image (nonsuperimposable on its mirror image) ○ Achiral­ superimposable on its mirror image and has a plane of symmetry (meso compound;  reviewed later in this study guide)


How do you draw chair conformations with substituents?



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● Steps for assigning configurations: 

○ Assigning priority 1­4, 4= lowest priority

○ Usually assigned by atomic number (higher atomic number=higher priority) ○ If 1­3 is going clockwise, the configuration is R.  If 1­3 is going counterclockwise, the  configuration is S.

● Reminder: A stereocenter is bonded to 4 DIFFERENT groups.

● When the lowest group, (#4) is not dashed, the configuration is switched. For example, if the  configuration from 1­3 is R but #4 is wedged, the configuration will be S instead.  ● For IUPAC naming for simple molecules, R/S in parentheses appear first in the name.  If the  molecule has two different stereocenters with different configurations, the R/S appear in  parentheses next to their specific orientation.  


How do you know if its r or s configuration?



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○ Ex: (S)­1­Bromo­1­chloroethane; (R)­3­Bromo­(S)­chloropentane

● Double and triple bonded substituents are treated differently 

○ C=C is treated as two C­C bonds

○ Carbon triple bonded to Carbon is treated as two C­C­C bonds.

● Stereoisomers 

○ Enantiomers 

■ Not superimposable 

■ A mirror image 

○ Diastereomers

■ Not superimposable

■ Not a mirror image (usually a change to one stereocenter instead of all) ● Meek compound

○ Has chiral centers that is achiral

○ It is superimposable on its mirror image and has a line of symmetry  Don't forget about the age old question of What is the meaning of the consumer problem in economics?

○ Meso compound only has a mirror plane if it is in eclipsed conformation  ● Fischer Projections

○ Drawing a molecule with straight horizontal and vertical lines. Horizontal lines are wedged  bonds (coming towards you) and vertical lines are dashed bonds (going away from you)

● To calculate how many stereocenters a compound will have= 2 to the nth power (n= number of  chiral centers)

● To calculate how many pairs of enantiomers the compound will have= 2 to the nth power divided by 2. 

● Conformers­ can be interconverted by a single bond without breaking that bond. (Alternative of  the same molecule)

● Constitutional Isomers­ have the same molecular formula but different atom connectivity ● Stereoisomers­ have the same molecular formula and the same connectivity but cannot be  superimposed or interconverted via a single bond rotation

● For enantiomers, both chiral centers will have opposite configuration names and for  diastereomers, only one chiral center will have opposite configuration names. Resonance Structures (Review)

● Two or more forms of the same molecule, but changing the placement of electrons ● Curved arrow always shows the flow of electrons We also discuss several other topics like What did muhammad wanted to remove out of the kaaba?
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● Three basic moves that are allowed for resonance structures=

○ Double bond to a lone pair

○ Lone pair to a double bond

○ Moving the double bond

● The structure becomes less important when it contains too much charges ● Don’t forget the OCTET RULE!

● More stable when the negative charge is on the more electronegative atom, and the more polar  atom.

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