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13 Cards in this Set
- Front
- Back
- 3rd side (hint)
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Isomers are? |
2 DIFFFERENT molecules with the same molecular formular (number and type of atoms) structural (constitutional) isomers - differ in the way their atoms are connected Stereoisomers - differ in the way their atoms are aranged in space |
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dghgh |
dhdh |
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fdhdh |
fdhdh |
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Tartaric acid has? |
2,3-dihydrobutanedioic acid
has 2 chiral centers that have the same 4 substituents (R, OH, H, CO2H)
meaning 2^2 stereoisomers = 4 possible stereoisomers
2 steroisomers = identical due to a plane of symmetry (picture) - therefore, only 3 stereoisomers
2 = enantiomers (cannot superimpose, mirror images)
3rd is achiral diastereomer
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A meso compound is? |
an achiral diasteromer of chiral steroisomers (optically inactive) an internal plane of symmetry exists when you draw a line that cuts the molecule in half MeSo = Mirror of Symmetry |
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Conformational isomers are? |
isomers which differ only by rotation about single bonds
result: substituants (ligands = attached atoms or groups) can be:
maximally close (Eclipsed conformation) Maximally apart (anti or staggered conformation)
anywhere (gauche conformation)
All conformations occur at room temperature
anti (staggered) conformation is the most stable = minimal electron shell repulsion
NOT TRUE ISOMERS |
conformers rotate around single bonds |
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When viewing different conformations of the same molecule (conformational isomers), what is the term when you view it from: a) above and from the right?# b) along carbon-carbon bond axis |
above and right: sawhorse projection along C-C axis: Newman projection |
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The lowest, most stable conformation of ethane is? why? the highest energy, least stable onformation of ethane is? why? another note: what is the bond hybridisation status of the carbons in ethane. why? |
staggered: when all 6 carbon-hydrogen bonds are as far away as possible because of outer shell repulsion (ESR) high energy = all 6 C-H bonds areas close as possible = eclipsed (eclipses are rare..) in between = infinate number of possibilities of conformations SP3 hybridised - 1 carbon, 4 bonds. tetrahedron. picture shows highest energy states and lowest energy conformations. |
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which of these rows is gauche conformation, eclipsed conformation, anti-conformation? why? note - rotation is based on the C2-C3 bond there are 4 C's this is butane |
row 1: anti-conformation. most energetically stable. the two far away hydrogens are opposite sides of the single bond. the two CH3's are far away from eachother as possible = staggered row 2: eclipsed. even though the CH3's aren't on the same side, there's an equal number of substituants or each chiral C on each side of the bond (based on fischer projection) row 3: gauche formation: not eclipse, but also not the most energetically stable, as the CH3's aren't as far apart as possible row 4: eclipsed - substituants are in the same plane as one another |
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how many anti-conformations are possible per bond? how many eclipse formations are possible? |
1 anti conformation - the most energetically favorable. the two methyl groups are furthest apart - 180 degrees from eachother = antiperiplanar first eclipsed conformation = when 2 Hydrogen + methyl group's line up, and a H + H line up. |
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what is the rotational barrier (barrier to rotation) in conformers? |
activation enery required to interconvert all the "rotomers" different forms |
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hoow many rotamers does butane have? |
3: 2 gauche conformers and an anticonformer barrier to rotation applies here: the gauche conformers require energy to return to anti-conformer the ommited conformation (eclipse) does not require energy to return to gauche or anti the 3 eclipsed conformations are NOT rotamers - they are transition states. 3 eclipsed have angles between the planes (=dihedral angles) of 120 degrees, 0, 120 degrees (= 240 degrees from first exclipse) |
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Dihedral angle = gauche means? anti means? eclipsed means? |
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