Intro to Spectroscopy

1
Lecture 4

• 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

2
Organic Chemistry From Yesterday to Today

• Late 1700s Atomic Theory

1800s Organic Structural Theory - Combustion
Analysis - Functional Group Tests
1900s Synthesis and Analysis
Today Automated Synthesis Spectroscopic
Analysis
3
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

4
Types of Spectroscopy

• NMR (Nuclear Magnetic Resonance Spectroscopy)
• Uses radio waves (electromagnetic radiation)
• Interacts with samples 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

5
1H NMR Spectrum of Ethanol
CH3CH2OH
ppm
6
IR Spectrum of Hexanol
Transmittance
Wavenumber (cm-1)
7
Mass Spectrum of Phenetole

94
Intensity
122
77
m/z (mass to charge ratio)
8
Ch 12 Spectral Unknown

• Be sure not to mix this unknown up with the
  Recrystallization Ch 4 unknown!
• 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.

9
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
10
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)
11
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
12
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
13
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
doesnt affect the HDI calculation Calculation
(in class)
Possible Compounds