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Infrared Spectroscopy Table quiz

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  • What are the two main things you need to know for each IR absorption?
    You need to know the wave number (frequency) at which it absorbs and the shape of the absorption.
  • What is the general wave number range for double bonds in IR spectroscopy?
    Double bonds typically absorb up to about 2000 cm⁻¹.
  • What mnemonic is used to remember the order of carbonyl absorptions and what does it stand for?
    The mnemonic 'CORN' stands for Chloride (acid chloride), Oxygen (carboxylic acid/ester), R/H (aldehyde/ketone), and Nitrogen (amide).
  • How does conjugation affect the absorption wave number of a carbonyl group?
    Conjugation lowers the absorption wave number by about 20 cm⁻¹.
  • What is a 'banana bond' and how does it affect IR absorption?
    A banana bond occurs in small strained rings and increases the absorption wave number by about 100 cm⁻¹.
  • What is the typical absorption wave number for an alkene (C=C) bond?
    Alkenes absorb in the range of 1600–1650 cm⁻¹.
  • Where do acid chlorides typically absorb in the IR spectrum?
    Acid chlorides absorb at the highest carbonyl wave number, around 1790 cm⁻¹.
  • What is a complex carbonyl and give an example?
    A complex carbonyl is a functional group that shows more than one absorption, such as carboxylic acids or aldehydes.
  • What is the absorption range for triple bonds (alkynes and nitriles) in IR spectroscopy?
    Triple bonds absorb between 2100 and 2300 cm⁻¹, with nitriles slightly higher than alkynes.
  • At what wave number does the O-H stretch of a carboxylic acid typically appear?
    The O-H stretch of a carboxylic acid appears as a broad peak between 2500 and 3000 cm⁻¹.
  • How can you distinguish between an alkyne and a nitrile using IR spectroscopy?
    Nitriles absorb at a slightly higher wave number than alkynes, and the presence of nitrogen in the molecule indicates a nitrile.
  • What is the typical absorption for an sp3 C-H bond (alkane)?
    An sp3 C-H bond absorbs around 2900 cm⁻¹.
  • What is the absorption wave number for an aldehyde C-H bond?
    An aldehyde C-H bond absorbs at about 2700 cm⁻¹.
  • How does the IR absorption of alcohols compare to amines?
    Alcohols show a broader absorption, typically covering much of the 3000 cm⁻¹ region, while amines have smaller, less broad peaks in a similar range.
  • What should you do if your professor gives slightly different IR absorption values than those in the lesson?
    You should focus on the general trends and ranges, and tailor your knowledge to your professor's preferences as needed.