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Orgo 2 > exam 1 (Orgo 2) > Flashcards

exam 1 (Orgo 2) Flashcards

1
Q

1/2 amine/amide N-H stretches (IR)

A

primary: 2 peaks
secondary: 1 peak

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2
Q

overtone (IR)

A

secondary absorptions that are generally twice the frequency
(carbonyl (C=O))

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3
Q

aldehyde peak

A

2700-2830 cm-1 small doublet

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4
Q

higher bond energy

A

higher frequency (higher energy), higher cm-1

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5
Q

bond energy trend increase

A

single, double, triple
more EN

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6
Q

s character

A

stronger bond, higher frequency

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7
Q

DoU

A

(2+2C-H+N-X)/2

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8
Q

alcohol fragmentation

A

alpha + dehydration

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9
Q

amine fragmentation

A

alpha

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10
Q

ketone + aldehyde fragmentation

A

alpha + McLafferty (4 C!)

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11
Q

alpha mech

A

……………..⏺+……………………………….
C -❌- C - OH…………..➡️……..C = OH +
…………….- NH2………..➡️…….C = NH2 +
…………….= O……………➡️…….C ≡ O +

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12
Q

dehydration mech

A

…………❌……………………
C - C - OH…..➡️…..C=C
|………………………………..
H ❌…………………………..

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13
Q

McLafferty

A

H is 4 C away
……………………..⏺+
………………………O
………↙️⬅️⬅️⬅️||
……H………………C
……|⤵️……….↱/..\
R - C - C -❌- C…..R/H

⬇️

……..⏺+
……..O-H
……..|
……..C
…..//..\
… C….R/H

+ R-C=C

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14
Q

-15

A

*CH3

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15
Q

-18

A

H2O

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16
Q

-29

A

CH2CH3 or HCO

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17
Q

-35/37

A

Cl

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18
Q

-43

A

C3H7

/\

19
Q

-79/81

A

Br

20
Q

cm-1, m/z, ppm

A

IR, mass spec, NMR

21
Q

M:M+2 = 1:1 (mass spec)

A

Br

22
Q

M:M+2 = 3:1 (mass spec)

A

Cl

23
Q

IR: aldehyde > ketone

A

less e- donation, so more double bond character, making for a higher frequency

24
Q

angle strain in rings (IR)

A

more angle strain (less Cs), more energy, higher wavelength

25
Q

mass spec instrument range

A

can range from 60-1200 MHz, but usually 300-400 MHz

26
Q

anti-parallel spin state (NMR)

A

higher in energy, against B0, resonance

27
Q

as B0 increases in strength

A

applied resonance frequency strength increases (to bring the nuclei into resonance)

28
Q

induced field

A

Every nuclei in existence is surrounded by e-. The orbiting and circulating e- generate their own, tiny magnetic field. It shields the nuclei, making it require less radiofrequency (UPFIELD)

29
Q

downfield

A

deshielded, left, more radiofrequency

feels more of the applied field

30
Q

upfield

A

shielded, right, less radiofrequency

feels less of the applied field

31
Q

delta scale

A

used to standardize observed frequencies for NMR

remember resonance frequency is dependent on the strength of the applied B0

The x-axis of an NMR spectrum is called the delta scale. It shows the position of resonance of each nucleus relative to a standard (TMS) and has units of ppm.

32
Q

resonance frequency

A

the frequency that brings the NMR-active nuclei into resonance, dependent on nuclei itself and B0.

Directly proportional to B0.

33
Q

applied field

A

B0

34
Q

field anisotropy

A

the orientation of nuclei in the magnetic field determines the chemical shift

⬆️……….➡️……..🔄 …….⬅️
⬆️……⬆️….⬇️…………⬇️….⬆️
⬆️……….⬅️……..🔄……..➡️
B0

⬇️ shielding / ⬆️ deshielding
🔄 pi e- circulating

35
Q

field anisotropy - double bond

A

Pi bonds have electron current above and below the plane. The direction of the induced magnetic field by the pi-electrons is ADDED to the applied field through the hydrogen, therefore the hydrogen is DESHIELDED

⬆️……….➡️……..🔄 ………⬅️
⬆️……⬆️….⬇️…..=…….⬇️….⬆️
⬆️……….⬅️……..🔄……….➡️
B0

⬇️ shielding / ⬆️ deshielding
🔄 pi e- circulating

36
Q

field anisotropy - triple bond

A

the triple bond is like a cylinder so the pi-electrons completely circulate. Now the induced field is OPPOSING the applied field through the proton, making the proton SHIELDED from applied field

⬆️……….➡️……..🔄 …….⬅️
⬆️……⬆️….⬇️…|||…⬇️….⬆️
⬆️……….⬅️……..🔄……..➡️
B0

⬇️ shielding / ⬆️ deshielding
🔄 pi e- circulating

37
Q

field anisotropy - aromatics (rings)

A

aromatics have a lot of pi-electron density known as ring current

induced field is ADDED to the applied field (even more now) through the protons, they are DESHIELDED

⬆️……….➡️……..🔄 ………⬅️
⬆️……⬆️….⬇️…..♨……⬇️….⬆️
⬆️……….⬅️………🔄……….➡️
B0

⬇️ shielding / ⬆️ deshielding
🔄 pi e- circulating

38
Q

dihedral angles

A

J values descend from it

the angle between two bonds originating from different atoms in a Newman projection

greater dihedral angles = greater coupling constant

39
Q

cis/trans

A

Z/E

40
Q

diastereotopic protons

A

chemically non equivalent protons that each produce distinct chemical shifts.

Z/E and cis/trans

if there’s a stereocenter (SC) in a molecule, any CH2 group’s protons will also be diastereotopic…

  1. the effect is felt most strongly when the CH2 is directly next to the SC
  2. the proton signal may or may not be resolved on the NMR spectrum

A stereocenter is an atom, typically carbon, that has four attachments that are different from each other.

41
Q

axial and equatorial Hs interconversion in NMR is…

A

…very fast at room temperature, it is faster than the NMR time scale can detect, so they average to a SINGLET

42
Q

acidic protons (O-H, N-H) exchange…

A

…faster than the NMR timescale.

This is why alcohols and amines are typically contaminated with H2O or acidic or basic impurities. This can lead to proton exchange, which is very fast and results in an averaged uncoupled signal

43
Q

13 C NMR

A

same principles as 1H NMR!

NO SPLITTING due to low abundace of 13C

R4C singlet
R3C-H doublet
R2CH2 triplet
RCH3 quartet

**a proton decoupled 13C NMR tells you how many different carbons a molecule has!!

shielding and symmetry are same

44
Q

integration in 13C NMR…

A

means nothing, so no correlation between # of C and peak height

Orgo 2 (1 decks)

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