Transcript Hints on Column Chromatography

Lecture 4
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Intro to Spectroscopy
Ch 12: Spectral Unknown
HDI (Hydrogen Deficiency Index)
Lecture Problem 1 Due
This week in lab:
Ch 4: Recrystallization & Melting Point
Procedures 1 & 2
Ch 4 PreLab Due
Quiz 1
Next week in lab:
• Ch 4: Procedures 3 & 5
• Ch 5: Extraction, Procedure 1
• Ch 5 PreLab Due (Common Shelf Chemical Data Table!) & Quiz 2
Organic Chemistry: From Yesterday to Today
Late 1700’s: Atomic Theory
1800’s: Organic Structural Theory
- Combustion Analysis
- Functional Group Tests
1900’s: Synthesis and Analysis
Today: Automated Synthesis &
Spectroscopic Analysis
Main Types of Spectroscopy
Each type of spectroscopy has its value in determining/confirming the structure of a
compound. Spectroscopy allows us to “see” the molecule.
NMR (Nuclear Magnetic Resonance):
• Aids in the determination of bond connectivity within a molecule & the pieces of a
molecule
IR (Infrared):
• Confirms the presence of functional groups within a molecule
MS (Mass Spectrometry):
• Determines the mass of a compound
• Also aids in the determination of pieces of the molecule
Types of Spectroscopy
NMR (Nuclear Magnetic Resonance Spectroscopy):
• Uses radio waves (electromagnetic radiation)
• Interacts with sample’s nuclei in the presence of a magnet
• Effect: nuclei flip and relax (known as resonance)
IR (Infrared Spectroscopy)
• IR radiation
• Interacts with molecule as a whole
• Effect: bond vibrations within molecule
MS (Mass Spectrometry)
• No radiation used
• Interacts with and destroys molecule; fragments molecule
• Effect: creates ions and neutral fragments of molecule
1H
NMR Spectrum of Ethanol
CH3CH2OH
ppm
IR Spectrum of Hexanol
Wavenumber (cm-1)
Mass Spectrum of Phenetole
94
OCH2CH3
MW = 122
122
77
m/z (mass to charge ratio)
Ch 12: Spectral Unknown
Be sure not to mix this unknown up with the Recrystallization Ch 4 unknown!
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1H
NMR spectrum - run and acquire data
IR spectrum - run and acquire data
MS - make up sample and submit sample for analysis
Be sure to get your spectral data signed and dated by the TA.
Sign up for time now.
Make up your samples during your scheduled lab period. Refer to the back inside
cover of the Lab Guide for sample prep instructions.
Store samples in the Instrument Room - be sure to label your samples!
Use melting point to get a list of possible unknowns (website).
Note:
Progress Check is due the week of March 20.
Final Report is due the week of April 24.
HDI (Hydrogen Deficiency Index)
HDI:
• Determines if a multiple bond or ring is present in a molecule
• Need molecular formula to determine HDI
• Good tool to use when determining possible structures of an unknown
• Coupled with spectral data - process of elimination from possibilities list!
HDI Calculation:
1. Determine the Hydrogen Deficiency (HD)
2. Determine HDI: HDI = HD/2
Hydrogen Deficiency
Hydrocarbons (C & H):
Example: Determine the HDI of a compound whose MF is C5H10. What are
possible structures for this compound?
Calculation (in class):
HDI
Hydrocarbons (C & H):
Example: Determine the HDI of a compound whose MF is C5H10. What are
possible structures for this compound?
The possible structures of the compound are:
Nitrogen and HDI
Nitrogen Organic Compounds (C, H & N)
Example: Given a MF of C4H7N, what is the HDI of this compound?
Rule: Count N as NH and rewrite formula: C4H6NH
Calculation (in class):
Possible Compounds:
Oxygen and HDI
Oxygen Organic Compounds (C, H & O)
Example: Given a MF of C6H12O, what is the HDI of this compound?
Rule: MF stays the same (unlike nitrogen); Oxygen doesn’t affect the HDI
calculation
Calculation (in class):
Possible Compounds: