Exam 3 Slides Flashcards
(88 cards)
1
Q
spectroscopy measures
A
the interaction of light (electromagnetic radiation) and matter
2
Q
light exhibits
A
wave-particle duality
3
Q
the energy of light (photons) is directly proportional to its ________
A
frequency
4
Q
On a macroscopic scale, matter appears to exhibit
A
continuous behavior
5
Q
Matter on the molecular scale exhibits ____________
A
quantum behavior
6
Q
how can molecules store energy
A
- rotate in space
- bonds vibrate like springs
- e- occupy molecular orbitals
- each is quantized
7
Q
vibrational excitation
A
energy is temporarily stored as vibrational energy (and usually released as heat)
8
Q
When can a bond absorb a photon
A
if the photon has the same energy as the energy gap in the vibrational energy levels
9
Q
NMR region of electromagentic spectrum
A
Radio Waves
10
Q
Region of electromagnetic spectrum for IR
A
Infrared
11
Q
Region of electromagnetic spectrum UV-VIS
A
visible and UV
12
Q
Info obtained NMR
A
specific arrangement of all c and h atoms
13
Q
Info obtained IR
A
Functional groups
14
Q
info obtained UV-VIS
A
conjugated pi system
15
Q
2 kinds of vibrational excitation
A
stretching and bending
16
Q
vibrating bonds emit
A
IR radiation
17
Q
C-H bond will ___________ than C-O
A
- absorb a higher energy photon
- allows for functional group identification
18
Q
IR spectrophotometer irradiates sample w/ ____________
A
- all frequencies of IR light
- wavenumber vs % transmittance
19
Q
wavenumber dependent on
A
- bond strength
- masses of atoms sharing bonds
20
Q
fingerprint region
A
- 400-1500
- single bonds
21
Q
diagnostic region
A
- 1600-4000
- double/triple/bonds to H
22
Q
Hybridization
A
- sp3 lower than sp 2and sp
23
Q
Resonance ______ a stretching signal
A
lowers
24
Q
when a bond undergoes stretching vibration, ________ _________ also oscillates
A
- diplole moment
- oscillating dipole moment creates an electrical field surrounding the bond
25
greater bond polarity =
* stronger IR signals
* because more polar bond means greater opportunity for interaction between the waves of the electrical field and the IR radiation
26
\_\_\_\_\_\_\_ signals are observed w/ __________ vibrating
* strong
* multiple bonds of same type\
27
hydrogen bonding can _______ the o-h bond
* weakens
* causes o-h stretch signal broadening
28
O-H from carboxylic acid
very broad OH
broad C=O
29
NH2 (secondary amine) IR signal
Udder-like (2 udders)
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NH (primary amine) signal
single udder
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tertiary amine
no peak b/c no N-H group
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strength of n-h stretch signals
weak-medium
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a single molecule can only vibrate
* symmetrically or asymmetrically at a given moment
* CH2 and CH3 groups can also vibrate as a group and give multiple signals
34
double bond region
* 1600-1850 cm-1
35
triple bond region
2100-2300 cm-1
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x-h bond region
2700-4000 cm-1
37
USing IR to disginguish between two compounds
* useful when tracking reactions
* need to ID key functional grous and determine how their spectra are different
38
mass spectrometry
the study of the interaction between matter and an energy source
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mass spec is used to
determine molecular weight and molecular formula
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* steps of mass spec
1. compound is vaporized and then ionized
2. massess of the ions are detected and graphed
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most common ionizing source
electron impact ionization
42
electron impact ionization
* generates a high-energy intermediate that is both a ratical and a cation
43
Molecular ion
AKA parent ion
if the radical cation remains intact
highest m/z
44
fragmentation
* resulting fragments may undergo further fragmentation
* ionization process generates many different cations
45
amount the magnetic field impacts the fragment depends on
mass to charge ratio
46
m/z
* mass to charge ratio
* determining factor by which ions are separated from each other in mass spectrometry
47
base peak
tallest in mass spectrum, relative abundance 100
48
m+· peak ______ easily
fragments
49
Nitrogen rule
* odd massed M+· peak may indicate odd number of N
* even massed M+· may indicate even number of N atoms
50
\_\_\_\_\_% 12C
\_\_\_% 13C
98. 9
1. 1
Per C atom!!!!
51
C=
relative abundance m+1/m x 100
52
Molecules w C have
strong M+2 peak (24% 27C to 76% 35C
53
Bromine M+2 peak
equal in height to M peak
54
Alcohol fragmentation
* alpha cleavage
* dehydration
55
alpha cleavage
bond to the alpha position of the alcohol is cleaved to form resonance-stabilized cation and radical
56
dehydration
ejects water (mass M-18)
57
amines undergo \_\_\_\_\_
alpha cleavage
58
McLafferty Rearrangement
loss of an alkene fragment
happens in carbonyls
59
High res mass spec
* measures up to 4 decimal places
* distinguish molecules w/ same mass but different molecules
60
alkane formula
CnH2n+2
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degree of unsaturation
decreases number of H atoms by two
62
NMR
nuclear magnetic resonance spectroscopy
63
spectroscopy vs spectrometry
* spectroscopy, study the interaction between matter and electromagnetic radiations
* ovservation
* measure the resulting radiations and make calculations about that object with it
* quantitative
64
NMR spectroscopy
study of interaction between electromagnetic radiation and nucleus of an atom
65
Why is odd number of protons required
* They have to behave as if they were spinning, and odd protons will have a net nuclear spin
66
applying magnetic field
If the normally disorded magnetic moments of atoms are exposed to an B0 (magnetic field), their magnetic moments will align
67
α
with
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β
against
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increasing magnetic field strength
increases energy gap
70
Info NMR spectra contains
* number signals
* shift: signal location
* integration: signal area
* splitting pattern: signal shape
71
homotopic protons
* overlapping signals
* axis of rotational symmetry
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enantiotopic protons
* plane of reflection for protons
73
chair interconversion
* at room temp, chair interconversion occurs rapidly
* NMR not fast enough, average is observed
74
TMS
standard for NMR chemical shift
75
shift is calculated as
* a comparison to TMS
observed shift from TMS
/operating frequency of instrument
=shift
76
Shielded protons
have smaller magnetic force acting on them, so have smaller energy gaps and absorb lower energy radio waves
upfield
77
deshielding
electroneg atoms withdraw electrons from nearby atoms causing H to be surrounded by less electron density
raise energy (downfield)
78
Diamagnetic anistropy
when electrons in pi systems are subjected to external magnetic ield, they circulate a lot
79
diamagnetic shift impact
similar to deshielding for aromatic protons
mess of multiplets
80
integration
area, quantifies _relative_ number of protons giving rise to the signal
81
Key NMR rules
* equivalent protons cannot split eachother
* to split eachother, must be w/in 2-3 bonds
* n+1 rule only applies to equivalent protons
82
coupling constant
(J) degree to which neighboring proton will shield/deshield its neighbor
when protons split eachother, coupling constant will be equal
83
isolated ethyl group gives what signal(s)
* triplet and quartet
* must have same coupling constant
84
integration of 9 indicates
tert-brtyl group (3 ch3 groups)
85
isolated isopropyl gives
doublet and a septet
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complex splitting
* occurs when nonequivalent neighboring protons split
* triplet of quartets
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labile H
* protons bonded to carbon split but hydroxyl proton is not
* undergoes rapid exchange w/ trace amts of acid
* blurs shielding/deshielding affect
88
build molecule
* HDI
* number signals
* integration
* draw fragments and put together
