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Isomers
Have the same molecular formula but different structures
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There are two types of isomers name them
Constitutional/structural isomers & Stereoisomers
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Inspection of molecular models of disubstituted cycloalkanes in which the two substituents are located on different carbons shows that ___ isomers are possible in each case.
two
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In one isomer, the two substituents are positioned on the same face, or side, of the ring; in the other isomer, they are on opposite faces. Substituents on the same face are called ______; while those on opposite faces are called _______
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We can use hashed-wedged line structures to depict the three dimensional arrangement of substituted cycloalkanes. Hashed bonds depict a substituent going _______ while solid dash wedged substituents depict them going _____.
- backward (behind the plane of the page)
- forward (protruding from the the plane)
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You and your mirror image are not identical and thus are ____________.
non-superimposable
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Define non-superimposable and give an example of the concept
- Definition: This means that molecules cannot be placed on top of one another and give the same molecule
- Example: If you reach out to your mirror image with your right hand, it reaches back with its left hand, and no matter how you rotate and maneuver your hand, you can never superimpose one on the other with the palms facing the same direction and the back of the hands facing the same direction
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Constitutional isomerism describes:
aka Structural isomers: Compounds that have identical molecular formulas but differ in the order in which the individual atoms are connected, resulting in completely different compounds
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An example of constitutional isomerism would be ethanol (CH3CH2OH) and methoxymethane (CH3OCH3). They both share the empircal formula _______, however, the subtle difference in order results completely different molecules. State two possible differences
- C2H6O
- melting points, boiling points, refractive indices etc
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Stereoisomerism describes isomers whose atoms are connected in the same _______ but differ in their _______ arrangement.
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Some isomers are mirror-image stereoiosmerism, and because of this they are said to have handedness, explain
The isomers are mirror images of each other but not superimposable, very much like the example with the hand reaching out to the mirror
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A molecule that is non-superimposable on its mirror image is said to be ______. Each isomer of the image-mirror image pair is called ________
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Structures that are superimposable on their mirror images are _______.
achiral
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All chiral structures contain an atom that is connected to four _______ substituent groups. Such a nucleus (atom) is called the ________ and is denoted by an ________
- DIFFERENT
- stereocenter or asymmetric atom
- asterik
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Molecules with one stereocenter are always _______
chiral
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Many chiral objects and molecules do not have _______ such as spiral staircases. What is the ONLY criterion for chirality
- stereocenters
- The non-superimposable nature of the object and mirror image.
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State 4 examples of chiral objects
State 4 examples of achiral objects
- chiral: shoes, ears, screws, spiral staircases, human body
- achiral: balls, ordinary water glasses, hammers (with identical ends), nails
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The foolproof method of determining chirality is to construct molecular models of the molecule and its mirror image and look for _______. However, faster method is to look for _______ in the molecule under investigation
- superimposability
- symmetry
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When looking for symmetry, we draw two planes of symmetry that bisect the ________and two _______. If they are all symmetrical, the structure is _______
- stereocenter & two substituents
- achiral
- *(a) is achiral and (b) is chiral
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Conformational isomers
A form of stereoisomerism in which the isomers can be interconverted just by rotations about formally single bonds (refer to figure on single bond rotation).
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Configurational isomers
stereoisomers that can cannot be converted into one another by rotation around a single bond
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Thought experiment: Work your through the various forms of isomers covered thus far and cross reference with the chart
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Fischer projection
a simplified way of depicting tetrahedral carbon atoms and their substituents in two dimensions
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With Fischer projections, the molecule is drawn in the form of a cross with the ______ ______ being at the point of intersection. The horizontal lines signify bonds directed _______ the viewer; the vertical lines signify bonds directed _______ the viewer. Hashed-wedged line structures have to be arranged in this way to facilitate their conversion into Fisher projections.
- central carbon
- toward
- away (from)
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Chirality & Stereochemistry explanation video: https://www.youtube.com/watch?v=yZ8JDDnyxC4&list=PLaySzQJTCO1nsM3ItT8irQ650tYgjHk6i
Chirality & Stereochemistry cheat sheet: http://leah4sci.com/wp-content/uploads/2015/10/Chirality-Stereochemistry-Cheat-Sheet-Study-Guide.jpg
GOOD LUCK!
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