Exam 1 Flashcards
Spectroscopy
The measurement of light (or electromagnetic radiation)
λ
Wavelength
One complete wave cycle
![](https://s3.amazonaws.com/brainscape-prod/system/cm/349/996/513/a_image_thumb.png?1624990322)
ν
Frequency
The number of cycles per time period
ν = c / λ
ν ~
![](https://s3.amazonaws.com/brainscape-prod/system/cm/349/997/030/q_image_thumb.jpg?1624990458)
Wavenumber
ν ~ = 1 / λ
E
Energy
E = hν = hc / λ
UV, X Rays, Gamma Rays +
Ionization
Visible, near UV
Electronic Transitions
Infrared (IR)
Molecular Bond Vibration
** IR Spectroscopy **
Microwave
Rotational Molecule Motion
Radio
Nuclear Spin Transitions
** NMR Spectroscopy **
What is the function of IR Spectroscopy?
To identify functional groups on an unknown molecule by looking at differences in molecular vibrations.
What determines the X and Y position s of peaks in IR spec?
X: Determined by Beer’s Law ( A = ɛ c l) and Bond Polarity (more polar bonds are more deshielded = higher ppm) that change the frequency
Y: Determined by the mass of atoms in the bond (heavier atoms = higher ppm) and the bond strength (stronger bonds are more shielded = lower ppm)
Affect of Resonance on IR Spec Peaks
Broaden peaks
Lowers frequency = higher ppm
Affect of Hydrogen Bonding on IR Spec Peaks
Broadens peaks
(ex: O-H peak)
What happens with symmetrical molecules in IR Spectrums?
Not seen because a dipole moment is needed to see a peak in IR
Shielding
More electron density = less interaction with magnetic field = lower ppm = upfield = more shielded
Less electron density = more interaction with magnetic field = higher ppm = downfield = less shielded (deshielded)
![](https://s3.amazonaws.com/brainscape-prod/system/cm/350/000/631/a_image_thumb.png?1624995318)
What is required for a bond to be IR active?
- Applied radiation E needs to match the energy of a bond stretching or bending.
- Needs to result in a change in molecular polarity.
What is Beer’s Law?
A = ϵ c l
A = abosrption (intensity of peak on Y-axis)
ϵ = molar absorptivity constant (change in polarity)
c = concentration
l = path length (thicker sample = more absorption)
IR Template
![](https://s3.amazonaws.com/brainscape-prod/system/cm/350/001/504/q_image_thumb.png?1624995368)
![](https://s3.amazonaws.com/brainscape-prod/system/cm/350/001/504/a_image_thumb.png?1624997063)
Ester / Ether
C - O Stretch
1200 - 100
Strong peaks
![](https://s3.amazonaws.com/brainscape-prod/system/cm/350/002/936/a_image_thumb.gif?1624997158)
Aromatic Ring
C = C Stretch
1700 - 1500
Variable peak with Overtones to the Left
![](https://s3.amazonaws.com/brainscape-prod/system/cm/350/002/950/a_image_thumb.gif?1624997316)
Alkene
C = C Stretch
1680 - 1620
Variable Peaks
![](https://s3.amazonaws.com/brainscape-prod/system/cm/350/003/197/a_image_thumb.gif?1624997430)
Ester
C = O Stretch
1750 - 1735 cm-1
~1735 cm -1
Strong Peak
![](https://s3.amazonaws.com/brainscape-prod/system/cm/350/003/300/a_image_thumb.gif?1624997584)
Aldehyde
C = O Stretch
1740 - 1690 cm-1
~1725 cm-1
Strong Peak
![](https://s3.amazonaws.com/brainscape-prod/system/cm/350/003/376/a_image_thumb.gif?1624997690)
Ketone
C = O Stretch
1750 - 1680 cm-1
~1710 cm-1
Strong Peak
![](https://s3.amazonaws.com/brainscape-prod/system/cm/350/003/435/a_image_thumb.gif?1624997783)
Carboxlyic Acid
C = O Stretch
1780 - 1710 cm-1
~1710 cm-1
Strong Peak
![](https://s3.amazonaws.com/brainscape-prod/system/cm/350/003/501/a_image_thumb.gif?1624997870)
Amide
C = O Stretch
1690 - 1630 cm-1
~1650 cm-1
Strong Peak
![](https://s3.amazonaws.com/brainscape-prod/system/cm/350/003/706/a_image_thumb.png?1624998019)
Alkyne
R - C ≡ C Stretch
2260 - 2100
Variable Stretch
![](https://s3.amazonaws.com/brainscape-prod/system/cm/350/003/873/a_image_thumb.gif?1624998141)
Nitrile
R - C ≡ N Stretch
2260 - 2220
Medium Peak
![](https://s3.amazonaws.com/brainscape-prod/system/cm/350/003/983/a_image_thumb.png?1624998224)
Alkyl sp3
C - H Stretch
2950 - 2850
Jagged Strong Peaks
![](https://s3.amazonaws.com/brainscape-prod/system/cm/350/004/073/a_image_thumb.jpg?1624998375)
Alken sp2
C - H Stretch
3100 - 3010
Medium Peaks
![](https://s3.amazonaws.com/brainscape-prod/system/cm/350/004/148/a_image_thumb.jpg?1624998464)
Carboxlyic Acid
O - H Stretch
Centered ~3000
Broad, Strong/Variable Peak
![](https://s3.amazonaws.com/brainscape-prod/system/cm/350/004/212/a_image_thumb.gif?1624998577)
Alcohol
O - H Stretch
3550 - 3200
Very Broad, Strong Peak
![](https://s3.amazonaws.com/brainscape-prod/system/cm/350/004/318/a_image_thumb.gif?1624998667)
Amine
R - N - H Stretch
3500 - 3300
Medium Peak
** One Peak w/One Terminal H, Two Peaks w/Two Terminal H’s **
![](https://s3.amazonaws.com/brainscape-prod/system/cm/350/004/451/a_image_thumb.gif?1624998758)
Amide
N - H Stretch
3700 - 3500
Medium Peaks
![](https://s3.amazonaws.com/brainscape-prod/system/cm/350/004/521/a_image_thumb.jpg?1624998871)
Alkyne
R - C ≡ H Stretch
~3300
Variable Peak
![](https://s3.amazonaws.com/brainscape-prod/system/cm/350/004/584/a_image_thumb.gif?1624998974)
What information is provided by mass spectrometry?
- Molecular weight of compound
- High resolution MS = gives molecular formula
- Some bond connectivity information (mroe from ‘H NMR)
What is being measured in MS?
The mass of ions (generally cations)
Cation Generation
Electron Impact (EI) Ionization
** Creates the radical cation represented in M+ Peak **
Easiest Electrons to Ionize
- Lone Pair electrons
- Pi electrons (triple/double bonds)
- Sigma electrons (single bonds)
What does Fragmentation Depend On?
- Carbocation Stability: the compound will fragment at the spot that creates the most stable C+ firstmost
** Substitution, Induction Effect, and Hyperconjugation affect C+ stability **
- Radical Stability: when mutliple stable C+ are possible, then the more stable radical will be made secondarily
Carbocation Stability
![](https://s3.amazonaws.com/brainscape-prod/system/cm/350/004/885/a_image_thumb.png?1625000064)