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Chemistry (UNI) > Organic Chemistry > Flashcards

Organic Chemistry Flashcards

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1
Q

how do hybrid orbitals form?

A

when s and p orbitals are close in energy they merge together to form hybrid orbitals

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2
Q

What are sp3 orbitals?

A

when 1s joins with three 2p orbitals, this is tetrahedral

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3
Q

what is sp2?

A

When 1s joins with two 2p orbitals, this is planar

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4
Q

What are sigma bonds?

A

sigma bonds are bonds formed between hybridised orbitals

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5
Q

What are pi bonds?

A

they are bonds formed between unhybridised 2p orbitals in the same plane (different plane to the sigma bonds)

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6
Q

What bonds are in double/triple bonds?

A 
double = 1 sigma, 1 pi
triple = 1 sigma, 2 pi
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7
Q

Describe orbitals and bonding in benzene

A
  • Each carbon has four e-
  • Each carbon is sp2 hybridised, each form 3 sigma bonds
  • each carbon has an extra p orbital, all of which form a pi system
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8
Q

Describe the properties of an aromatic compound

A
  • Must be cyclic
  • Have a pi system (each atom must have an unhybridised p)
  • Must be planar
  • must have 4n+2 pi electrons, where n is an integer
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9
Q

What happens when orbitals combine in phase?

A

form bonding bond (orbital spread over both atoms)

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10
Q

what happens when orbitals combine out of phase?

A

form anti-bonding bond (node between 2 phases where no electrons can exist)

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11
Q

anti-bonding and bonding occupy the same space

A

but electrons fill the lowest energy orbitals and so go into bonding orbitals

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12
Q

Rules of molecular orbitals?

A
  • No of Atomic orbitals = No of molecular orbitals
  • In phase AOs = bonding
  • out of phase AOs = anti-bonding
  • AOs overlap to form MOs
  • for efficient overlap, difference in AOs energy must be small
  • bond order = 0 means bond doesnt exist
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13
Q

Equation for bond order?

A

bond order = (# e- in bonding - # e- in antibonding)/2

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14
Q

What is meant by conjugated?

A

When 2 double bonds are separated by a single bond, the p orbitals overlap to form a pi system (must be planar for a pi system)

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15
Q

Why is benzene more stable?

A

the energy of bonding in benzenes MOs is less after conjugation making it more stable

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16
Q

Equation to find difference in energy between homo and lumo? What happens when the E is of the right wavelength?

A

Delta E = hv = hc/lamda

- energy of right wavelength = e- excited

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17
Q

What does it mean when a molecular is more conjugated?

A

more conjugated = smaller energy gap = larger wavelength

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18
Q

What do HOMO and LUMO stand for?

A

Highest occupied molecular orbital

Lowest unoccupied molecular orbital

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19
Q

why is the homo lumo gap important?

A

This is the smallest gap so it is where electrons are most likely to be excited

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20
Q

What does a smaller homo lumo gap mean?

A

more mobile pi electrons, therefore energy is more distributed over the molecule, stabilising it

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21
Q

ethene has 2 p electrons which can be in or out of phase

A

2 in or out of phase ethenes can combine in or out of phase, leading to 4 potential butadiene molecules

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22
Q

Why is butadiene more stable than ethene?

A

its homo lumo gap is smaller

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23
Q

What is pauling theory?

A

Pauling theory is the theory that the energy of a covalent bond between X and Y, is the mean of the energy of the covalent bond between X-X and Y-Y plus additional energy due to ionic factor (this additional energy is due to electronegativity)

24
Q

Why is CCl3COOH a weak acid?

A

The Cl- are v electronegative. This means that they pull e- density towards themselves, reducing e- density on the COO-, stabilising it

25
Q

What is a chiral compound?

A

a compound that isn’t superimposable on its mirror image

- chiral carbon has 4 different groups attached

26
Q

How can you tell whether a compound is chiral?
How can you tell the difference between enantiomers?
What is a racemate

A
  • chiral compounds rotate plane polarised light
  • enantiomers rotate light by the same amount but in different directions
  • racemates have no rotation
27
Q

Equation for specific rotation? units?

A

SR = angle/conc*path length
conc in g/cm3
path length is dm

28
Q

Dextro and laevo?

A 
\+ = clockwise = dextro
- = anticlockwise = laevm
29
Q

Name S and R isomers

A

1) Assign priority on an atom by atom basis
2) triple>double>single
3) Face lowest priority away from you
4) draw arrow from 1st to 2nd to 3rd
5) clockwise = R, anticlockwise = S

30
Q

What are diastereoisomers?

A

Stereoisomers that aren’t mirror images of each other and have more than one chiral centre

31
Q

3 methods for separating racemates?

A
  • separate crystals based on differences in their shapes
  • use stereospecific nature of enzymes to remove one of the enantiomers, unreacted enantiomer can by removed by distillation
  • Convert enantiomers into diastereoisomers and then resolve using ordinary separating techniques and then treat reagents to regenerate enantiomers
32
Q

What are conformers?

A

different shapes of the same molecule caused by rotation around a single bond

33
Q

Draw a staggered and eclipsed molecule? Which is lower energy?

A 
eclipsed = higher energy
staggered = higher energy
34
Q

What is a rotational barrier? Draw a molecule with a high rotational energy and why do some molecules have a high rotational barrier?

A
  • the activation energy required to rotate bonds

- High Ea to rotate bonds due to steric interference between groups

35
Q

What is ring strain? What does a higher strain mean?

A
  • The amount by which the bind angles arent 109.5

- more strain = higher energy

36
Q

Between straight chain molecules there is a constant enthalpy of combustion, what does this show?

A
  • molecules rotate to minimise strain, into their lowest energy configuration
  • as cyclic molecules get bigger they can rotate to minimise strain
37
Q

Describe SN1? draw graph
Describe the TS
What favours SN1?

A
  • First order
  • Rate is independent of the nucleophile
  • 2 transition states and a carbocatian
  • TS = 4 coordinate, 1 stretched bond
  • Stereochemistry can be retained or inverted
  • more stable carbocatian = increased rate of SN1
  • polar solvents favour SN1 because TS/carbocatian are lower energy
  • Tertiary Halogenoalkes more likely to SN1 because more stable carbocation
38
Q

Describe SN2? Draw Graph
Describe the TS
What favours SN2?

A
  • Second order
  • Rate dependent on nucleophile
  • TS = 5 coordinate, 2 stretched bonds
  • Stereochemistry is inverted
  • Large groups block Nu, decreasing SN2
  • Primary halogenoalkanes favour SN2 (less steric hindrance, so Nu can get to molecule)
39
Q

Why are strong bases bad leaving groups?

A
  • don’t want to accept electrons
40
Q

Why do aprotic solvents favour E2 and SN2

A

they are less likely to have hydrogens floating around to join carbocation in SN1/E1

41
Q

Draw graph for E1 and E2

A

Fun

42
Q

Draw SN1/SN2 mechanism

A

FUN

43
Q

Draw E1/E2?

A

LEARN

44
Q

Why are SN1 and E1 first ordeR?

A

second steps are fast and so arent the RDS

45
Q

E1 VS SN1

A
  • entropy favours E1 as there are more products
  • stronger bases favour E1
  • weak bases favour SN1
46
Q

What happens when you replace C-H with C-D bond, with regards to mechanism rates?

A

rate of E2 goes down but E1 is unaffected. This is because the breaking of the C-D bond isnt in E1 RDS. Rate of E2 goes down becasue Ea for C-D bond is 5KJ/mol higher than C-H

47
Q

What is regioselectivity?

A

Where the double bond ends up, forms a major and minor product

48
Q

What is stereoselectivity?

A

arrangement of groups around double bond, a product based on kinetic/thermodynamic control

49
Q

what is stereospecificity?

A

one isomer based on the mechanism and stereochemistry

50
Q

E1 Vs E2

A

E1 is stereoselective and regioselective

E2 is stereospecific and regioselective

51
Q

How do conformers affect carbocations? Draw pictures

A

configuration is eclipsed or staggered (steric hinderance)

52
Q

elimination vs substitution

A

E1 and E2 are regioselective, therefore more substituted alkenes will go via elimination because the transition state will be more stable

53
Q

What is antiperiplanar?

A
  • configuration where hydrogen and LG are in the same plane but opposite sides
  • This is the optimum configuration for E2
54
Q

What is a stereoselective reaction?

A

give one a major product because the reaction has a pathway choice. Either a path with a lower activation energy (kinetic control) or one with a more stable product (thermodynamic control)

55
Q

What is a stereospecific reaction?

A

Lead to the production of a single isomer due to the stereochemistry of the starting material and the mechanism of the reaction. NO CHOICE. The reaction gives a different diastereoisomer of the product from each stereoisomer of the starting material

56
Q

What determines whether substitution or elimination?

A
  • bulky bases favour elimination
  • basicity (stronger favour elimination)
  • temperature (entropy) favours elimination
  • avoiding steric hinderance in the product (more stable product) release of strain favours elimination
  • steric hinderance of delta + C favours elimination
57
Q

What is regiospecificity

A

Forms one singular product

Chemistry (UNI) (6 decks)

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