Home Podcasts THMG111 – Functional Groups: Alcohols

THMG111 – Functional Groups: Alcohols


In this episode, Bob and Mike discuss alcohols, which are part of functional groups.

Complete Show Notes

4:45 What is a Functional Group?

  • Group of atoms that attach to a saturated carbon atom or organic molecule and function in a similar way – called hydroxyl groups
  • Most common example is alcohol, which is a functional group comprised of an O and H together attached to a carbon molecule
  • Ethanol (grain alcohol) is the functional group we know best:
    • “Eth” means 2 carbons, “an” indicates a single bond, and “ol” refers to an OH functional group – C2H5OH

10:15 Solubility

  • The “oh” in the alcohol gives it a similar solubility to water – it’s hydrophilic (water-loving)
  • The addition of a functional group doesn’t make it miscible – instead, it only increases its solubility
  • In smaller molecules, the solubility becomes 100%
  • We see this frequently in methane to methanol and propane to propanol (rubbing alcohol)
  • However, in larger molecules, the OH starts to become weaker when compared to the larger, non-polar partner
  • Example:
    • Magnets are attracted to each other – take 100 pieces of a 1-inch piece of wood and glue magnets to the end of them
    • Doing this would allow us to get the pieces of wood to stick together
    • If we use bigger pieces, there’s less of a chance the magnet will find another magnet on the wood, so less of the wood will stick together

13:15 Boiling Temperatures

  • The OH group can also increase the boiling temperature – related to the function of the OH group in a manner that’s very similar to solubility
  • With solubility, the magnetism allows everyone to play together
  • With OH, hydrogen bonding (or Van der Waals force) keeps the alcohols sort-of connected together – this means it takes more energy to get the molecules into the atmosphere and that it will take a higher temperature to get them to vaporize
  • Methane and propane are gasses, but propanol and methanol are liquids – this means they have lower vapor pressures than their parent carbon chains

17:20 Flammability

  • Like solubility, smaller OH tends to be more flammable than larger OH – the longer the carbon chain, the less flammable it becomes
  • However, the addition of OH to the carbon chain does widen the flammable range by a few percentage points on the lower and upper ends
  • Keep in mind that alcohols burn clear – methanol is a rare exception because it burns blue (which can be masked in broad daylight)

20:20 Toxicity

  • Vaporizing substances can be irritating to our eyes and nose – they don’t play well with mucous membranes
  • Larger carbon structures tend to be less toxic than smaller ones – some OH are completely nontoxic, though (like ethylene glycol)
  • While the alcohol functional group OH has relatively low toxicity when attached to a carbon chain, that’s not the case with a hydroxyl radical
  • If you have an OH in the formula, don’t just assume it’s safe – only non-toxic if it’s connected to a carbon chain
  • Hydroxyl groups are very dangerous and can cause serious tissue and genetic damage

25:30 Where Do We Find Alcohol Functional Groups?

  • Typically found in a liquid form
  • Not like to find them as a gas due to hydrogen bonding
  • Even the smallest methanol has a BP of 137 degrees Fahrenheit
  • OH is commonly found in steel or stainless-steel containers, drums, carboys, and 406, 407, and chemical carriers

26:30 Where Do We Find OH Functional Groups?

  • Used as fuels, disinfectants, solvents, and cleaners
  • One of the most common functional groups – nature uses it almost like a linking mechanism
  • One example is fatty acids, where the two chains connecting OH are linked together when the OH is removed from the carboxy group at the end of the chain

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