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Organic Chemistry > Exam 2 > Flashcards

Exam 2 Flashcards

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1
Q

Electromagnetic Radiation

A

light has both wave like and particle like properties

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2
Q

What is wavelength?

A

distance from peak to peak
- smaller wavelength = higher energy

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3
Q

What is frequency?

A

time to get from one peak to the next, higher frequency = higher energy

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4
Q

Which frequency of light has the highest energy?

A

gamma rays

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5
Q

Which frequency of light has the lowest energy?

A

microwave radio

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6
Q

What information about a molecule can be determined by nuclear magnetic resonance (NMR)?

A

the specific arrangement of all carbon and hydrogen atoms in the compound
- radio waves

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7
Q

What information about a molecule can be determined by IR spectroscopy?

A

The functional groups present in the compound
- infrared

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8
Q

What information about a molecule can be determined by UV-VIS spectroscopy?

A

any conjugated pi system in the compound
- helps us measure concentration
- visible and ultraviolet

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9
Q

What light measures excitation of electrons?

A

UV/Vis

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10
Q

What light measures excitation of bond? (vibration excitation)

A

IR

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11
Q

What light measures rotation of molecules?

A

IR/NMR

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12
Q

What is the result of covalent bonds absorbing energy in the IR region?

A

molecular vibration (bending and stretching of the bond)

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13
Q

What determines the quantized energy of a bond?

A
  • bond type (single, double, or triple)
  • atoms attached
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14
Q

What does a higher wavenumber indicate?

A

higher energy

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15
Q

What is the wavenumber for a C-H bond?

A

~3000 cm−1

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16
Q

What is the wavenumber for a C-D bond?

A

~2200 cm-1

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17
Q

What is the wavenumber for a C-O bond?

A

~ 1100 cm-1

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18
Q

What is the wavenumber for a C-Cl bond?

A

~700 cm-1

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19
Q

What is the wavenumber for a C///N bond?

A

~2200 cm-1

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20
Q

What is the wavenumber for a C//N bond?

A

~1600 cm-1

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21
Q

What is the wavenumber for a C-N bond?

A

~1100 cm-1

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22
Q

What is the relationship between atom size, energy and wavenumber?

A

smaller atoms absorb higher energy/ higher wavenumber

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23
Q

What is the relationship between bond strength, energy, and wavenumber?

A

stronger bonds absorb higher energy/ higher wavenumber

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24
Q

Wavenumber of sp3 (alkane) hybridized carbon?

A

~2900 cm-1

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25
Q

Wavenumber of sp2 (alkene) hybridized carbon?

A

~3100 cm-1

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26
Q

Wavenumber of sp (alkyne) hybridized carbon?

A

~3300 cm-1

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27
Q

What is the effect of resonance on wavenumber?

A

resonance usually decreases the energy level of a bond by delocalizing electrons

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28
Q

What is the wave number of a ketone?

A

~1720 cm-1

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29
Q

What is the wavenumber of a conjugated ketone?

A

~1680 cm-1

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30
Q

Size of C-H peaks?

A

typically large

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31
Q

Efficiency in absorbing the IR radiation (dipole moment)

A

strong dipole = strong peak

32
Q

Result of bond with stronger dipole moment?

A

stronger peaks in the IR spectrum
- symmetrical molecule has no stretching peak

33
Q

What can lead to the broadening of a peak in an IR spectrum?

A

hydrogen bonding

34
Q

Size of peak for an alcohol diluted in a solvent that does not hydrogen bond?

A

peak is narrow

35
Q

Size of peak for an alcohol diluted in a solvent that does hydrogen bonding?

A

peak is broad

36
Q

How many peaks do primary amines have?

A

2 peaks

37
Q

How many peaks do secondary amines have?

A

1 peak

38
Q

What is mass spectroscopy?

A
  • doesn’t use electromagnetic radiation
  • bombards sample with electrons
39
Q

What is the primary use of mass spectroscopy?

A

to determine molecular weight and molecular formula

40
Q

How does a mass spectrometer work?

A
  • a compound is vaporized, then ionized, and undergoes fragmentation
  • the masses of the ions are detected and graphed
41
Q

Molecular Ion (M)*` - The radical cation

A
  • +1 charge on the radical cation
  • no change in mass
  • splits into an uncharged radical and carbocation (fragmentation)
  • sorted by mass to charge (m/z) ratio
42
Q

What is the base peak?

A

tallest peak

43
Q

(M+1)*` Peak

A
  • Due to heavier isotopes of common atoms like carbon
44
Q

(M+2)*` Peak

A
  • most often due to the presence of Cl or Br
  • second most abundant forms of Cl and Br have +2 mass
45
Q

What is NMR spectroscopy

A

Nuclear magnetic resonance spectroscopy
- most powerful technique for investigating organic compounds
- Interaction between electromagnetic radiation and atomic nuclei

46
Q

Which nuclei have a net nuclear spin?

A
  • nuclei with an odd number of protons and or an odd number of neutrons
47
Q

What is the result of nuclear spin?

A

creates a tiny magnetic field = magnetic moment

48
Q

When a strong external magnetic field is applied, the nuclei will align with or against the external field.
Aligning with =
Aligning against=

A

Aligning with = alpha spin
Aligning against= beta spin

49
Q

What does the energy difference between the alpha and beta states depends on:

A
  • strength of external magnetic fields
  • The electronic environment of the nuclei
50
Q

Is the alpha or beta spin state higher energy?

A

beta state

51
Q

What are the 4 key characteristics of the 1H NMR Spectrum

A
  1. # of signals
  2. chemical shifts
  3. integration
  4. shape/ multiplicity
52
Q

Number of signals =

A

number of chemically distinct protons

53
Q

Enantiopic Protons

A

Existence of a plane of symmetry means the H are equivalent

54
Q

Diastereotopic Protons

A

Not equivalent
- no plane of symmetry
- can’t rotate
*only when chiral center

55
Q

What is the equation for chemical shift?

A

observed shift from TMS in hertz / operating frequency of the instrument in hertz

56
Q

What happens to the chemical shift value when electron withdrawing groups are added to the atom?

A

It gets bigger

57
Q

How much does the chemical shift value increase with the oxygen of an alcohol or an ether?

A

+2.5

58
Q

How much does the chemical shift increase for oxygen of an ester

A

+3

59
Q

How much does chemical shift increase for a carbonyl group (C=O)?

A

+1

60
Q

Multiplicity/ splitting patern?

A

the number of peaks in a given signal

61
Q

Coupling constant/ J value?

A

the degree to which a neighboring proton will couple to its neighbor

62
Q

What is a diene?

A

compound with two double bonds

63
Q

Conjugated pi system

A
  • double bonds separated by one sigma bond
64
Q

Is a trans or a cis diene more stable

A
65
Q

HOMO

A

highest occupied molecular orbital

66
Q

LUMO

A

lowest occupied molecular orbital

67
Q

1,2-Adduct

A

kinetic product

68
Q

1,4-Adduct

A

thermodynamic product

69
Q

What are the types of pericyclic reactions?

A
  • electrocyclic
  • cycloaddition
  • sigma tropic rearrangement
70
Q

Cycloaddition

A

2 reactants –> 1 ring structure

71
Q

Electrocyclic

A

open chain —> cyclic structure

72
Q

sigmatropci rearrangement

A

cyclic rearrange but no ring

73
Q

Diels-Alder reaction

A
  • a [4+2] cycloaddition reaction
  • mechanism is cyclic and concerted
74
Q

Thermodynamics of Diels-Alder

A
  • forward reaction favored between 0-200C
  • Temperature >200 favors the reverse reaction (retro Diels-Alder)
75
Q

Diels- Alder Reactants

A

Diene + Dienophile
- Reaction is slow unless dienophile has an electron withdrawing group

76
Q

Stereospecificity of Diels- Alder

A
  • Diene must be in cis conformation
77
Q

Is the exo or endo position preferred?

A

endo (pointed down)

Organic Chemistry (10 decks)

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