Study Notes for CHEM 235-A: Organic Chemistry Laboratory I

CHEM 235-A: Organic Chemistry Laboratory I

Functional Groups and Nomenclature

Overview

  • Emphasis on understanding functional groups and nomenclatural conventions in organic chemistry.

Laboratory Steps for Organic Synthesis

Step 1: Reaction Set-Up

  • Objective is the synthesis of small organic molecules.

Step 2: Work-Up and Purification

  • Essential to isolate and purify the synthesized organic molecules post-synthesis.

Step 3: Structure Elucidation and Analysis

  • Analyzing the structure of synthesized compounds using spectroscopic methods.

Introduction to Functional Groups

The Electromagnetic Spectrum

  • Relationship between Wavelength and Frequency: They are inversely proportional.

    • Equation: C=vimesextλC = v imes ext{λ} where

    • CC = speed of light (approximately 3imes1010extcm/sec3 imes 10^{10} ext{cm/sec})

    • vv = frequency in hertz (Hz)

    • extλext{λ} = wavelength (cm)

  • Energy of a Photon:

    • Formula: E=rachextλE = rac{h}{ ext{λ}}

    • Define constants:

    • hh = Planck's constant = 6.62imes10−34extJs6.62 imes 10^{-34} ext{J s}

The Electromagnetic Spectrum Visualization

Spectrum Regions

  • Wavelength (nm): Ranges from gamma rays to radio frequencies.

  • Gamma - 10−210^{-2} nm to 10−310^{-3} nm

  • X-ray - 10−510^{-5} nm to 10−410^{-4} nm

  • UV - 10−410^{-4} nm to 10−310^{-3} nm

  • Visible - 400 nm to 700 nm

  • Infrared - 10−310^{-3} nm to 10−110^{-1} nm

  • Microwaves - 10−110^{-1} nm to 10010^{0} nm

  • Radio Waves - 10010^{0} nm to 10210^{2} nm

  • Frequencies in Hz

    • Visible frequencies range from 4.0imes1014exts−14.0 imes 10^{14} ext{s}^{-1} to 7.5imes1014exts−17.5 imes 10^{14} ext{s}^{-1}.

Molecular Interaction with Radiation

Effects of Radiation on Molecules

  • Various types of radiation can cause:

    1. Ionization (gamma rays, X-rays)

    2. Electronic transitions (UV radiation)

    3. Molecular vibrations (infrared)

    4. Rotational motion (microwave)

Infrared Spectroscopy

Basics of Infrared Spectroscopy

  • Frequency of IR Radiation: Matches bond vibrations in molecules.

  • The classical model considers vibration of two masses (atoms) connected by a covalent bond, acting like a spring.

    • Infrared Stretching Energies:

    • extC−Hext{C-H} stretch ~ 3000 cm⁻¹

    • extC−Dext{C-D} stretch ~ 2200 cm⁻¹

    • Stretching frequency formula: v = rac{1}{2}igg( rac{k}{m}igg)^{ rac{1}{2}}

    • Where:

      • kk = force constant of the bond

      • mm = mass of the atoms
        This model demonstrates that the frequency of radiation absorbed must be equal to the frequency of bond vibration for absorption to occur.

Ultraviolet-Visible (UV-Vis) Spectroscopy

Electronic Excitation

  • In UV-Vis spectroscopy, molecules can absorb energy, resulting in electronic excitation.

  • For example, transition from the ground state to the excited state can be represented as:

    • From extHOMOext{HOMO} to extLUMOext{LUMO}, where $ ext{HOMO}$ = Highest Occupied Molecular Orbital and $ ext{LUMO}$ = Lowest Unoccupied Molecular Orbital.

  • Energy required for excitation can be represented using the equation:
    E=hvE = hv

    • Position of absorbs and associated energies varies based on molecular structure.

Nuclear Magnetic Resonance (NMR) Spectroscopy

Principles of NMR Spectroscopy

  • An external magnetic field (B0B_0) aligns the nuclear spins of the sample.

  • Applying radio frequency energy can change the alignment of the nuclear spins, leading to observable signals in the spectrum.

    • Components:

    • (a) No external magnetic field: Random orientation of nuclear spins.

    • (b) With applied B0B_0: Nuclear spins align, producing a net magnetization.

Summary

  • Understanding functional groups is essential in organic chemistry as they define properties and reactivity of organic compounds. Major spectroscopic techniques provide insight into structural analysis and elucidation of organic molecules.