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49 Cards in this Set
- Front
- Back
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Define enantiomers. |
Molecules that are non-superimposable |
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What is an asymmetric carbon? |
A carbon with 4 different groups attached. |
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What is a stereocenter? Give an example. |
An atom at which the interchange of 2 groups a stereoisomer Asymmetric carbon |
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What is the element effect? |
The effect the identity of the atom the acidic hydrogen is attached to has |
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How does acidity vary across the periodic table? |
Increases to the right and down |
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What is the element effect? |
The effect the atom adjacent to the acidic hydrogen has on the acidity of a molecule |
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What is the charge effect? |
A positive charge on the atom bonded to the acidic hydrogen increases the acidity of the acid |
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What is the polar effect? How does this effect acidity? |
The effect that polar bonds in an acid have on the stability of the deprotonated ion which effects the acidity More acidic (electron withdrawing) and less acidic (electron donating) |
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Which of the 3 factors that determine acidity have a large effect? |
Charge and element effects |
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What shape do sp2 carbons adopt? |
trigonal planar |
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What shape do sp3 carbons adopt? |
tetrahedral |
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What shape do sp carbons adopt? |
linear |
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What is a pi star orbital? How does it form? |
An antibonding molecular orbital From the subtractive overlap of two 2p orbitals |
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How can a substituted hydrocarbon alkene have a dipole? |
sp2 carbons are more electronegative than sp3 carbons therefore polar bond formed |
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What increases the stability of an alkene (2)? |
trans formation and more substituents directly on sp2 cabrons (double bond) |
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What stabilises a carbocation? |
more substituents on positive carbon |
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When will a carbocation undergo rearrangement? |
To form a more stable carbocation (more substituents) |
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What catalyses alkene hydration? |
conc. strong acid |
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What is a diene? |
Compounds with 2 carbon-carbon double bonds |
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What is a conjugated diene? |
A compound where 2 double bonds are seperated by a single bond |
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Why are conjugated dienes more stable? |
delocalisation energy |
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What are allenes? |
Compounds with 2 adjacent double bonds |
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How can allenes undergo stereochemistry? |
The R-C-R bonds at either end are perpendicular therefore can form enantiomers |
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How do you assign R and S? (3) |
- Assign priorities to all groups - View molecule along asymmetric C-(lowest priority group) bond - Determine whether clockwise (R) or anti-clockwise (S) |
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How do the physical priorities of enantiomers compare? |
Identical except from roate plane polarised light in opposite directions |
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What is the absolute configuration of a compound? |
The actual 3D arrangement of atoms in space |
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What is a diastereoisomer? |
Compounds with 2 or more asymmetric carbons where only 1 group has been flipped |
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How do the physical priorities of diastereoisomercompare? |
Completely different |
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What is a meso compound? |
A compound with 2 or more asymmetric carbons that isn't chiral due to an internal plane of symmetry |
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What is amine inversion? What is it an example of? |
The rapid interconversion of stereoisomers about an asymmetric carbon Racemisation |
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What does a newman projection look like? |
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How do you draw a Fishcer projection? (3) |
- Arrange molecule in eclipsed conformation - view along (asymmetric carbon)-(group on plane of page) bond - Draw bond on plane of page vertically and others horizontally with groups on left and right from perspective described above |
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How do cis and trans conformations of cyclohexane in chair form exist? |
cis = both groups pointing up trans = one group up and one down |
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Are groups more stable in axial or equatorial positions in the chair conformation of cyclohexane? |
Equatorial |
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What are the 2 energy minima in the cycohexane conformations? |
chair and twist boat |
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When converting chair cyclohexane to planar how do you distinguish between the groups that were pointing up and down? |
Use wedges and dashes to show cis or trans conformation |
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When viewing a Fischer projection which bonds are going away from you and which are coming towards? |
Vertical going away and horizontal coming towards |
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In an acid-base equilibrium which side is favoured? |
The side with the weaker acid and base |
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What is s character and what causes it to vary? |
S character determines how close the electrons are held to the nucleus and the length of the bond (more s = closer=shorter bond) Determined by the level of sp hybridisation |
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What type of carbon has the least s character and what does this result in? |
sp3 = least s character = further = longest bond |
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How do you calculate the degree of unsaturation/unsaturation number? What does this tell you about the compound? |
U (no. of rings + multiple bonds) = (2C + 2 - H)/2 (Halogens and nitrogens count as H) |
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What occurs in the 2nd step of alkene addition? |
A carbocation accepts an electron pair from a nucleophile |
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What does Hammond's postulate state? |
The structure and energy of the transitionstatecan be approximated by the structure and energy of the intermediateKzT |
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What is a cumulene? |
A compound with a carbon involved in 2 double bonds |
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In a Fischer projection if H is on the hourizontal how does this effect drawing the stereochemistry? |
Flips it as H now coming towards you therefore for R = anti-clockwise and v.v. |
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What is the relationship between the two chair conformations of cyclohexane? |
Diastereomers |
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Define chirality. |
A compound that has a non-super imposable mirror image |
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What is the relationship between the two molecules that are rapidly interconverted between due to amine inversion? |
Diasteromers |
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Give an example of a polar aprotic solvent |
Acetone |
