Tag Archives: alkanes

Chapter 10: Organic reactions: pathways to new products

10.1 Reactions of Alkanes

Alkanes contain strong carbon-carbon single bonds and strong carbon-hydrogen bonds. There are no partial charges on alkane molecules that might initiate reactions. The effect is that alkanes only undergo very few reactions.

(1) Combustion of alkanes

Alkanes can undergo combustion, producing CO2(g) and H2O(g)

When asked to create a combustion equation for a particular fuel, do the following steps:

  1. Write the fuel’s molecular formula
  2. Add excess O2(g)
  3. Produce CO2(g) and H2O(g)
  4. Balance C, H and O in that order.
  5. REMEMBER TO INCLUDE ALL THE STATES!

General formula: alkane + O2(g) → CO2(g) + H2O(g)

Example: C6H14(l) + O2(g) → 6CO2(g) + 7H2O(g) (halves are okay!)

(2) Substitution of alkanes

Alkanes can also undergo substitution, in which one of the hydrogen atoms is replaced with a halogen (e.g. F, Cl, Br, or I).

General formula: alkane + X2 → chloroalkane

Example: CH3CH3(g) + Cl2(g) + UV light → CH3CH2Cl(g) + HCl(g) (note that HCl is a gas!)

10.2 Reactions of alkenes

(1) Addition of alkenes

Alkenes can under addition reactions with halogens, hydrogen gas or water.

addition reactions of alkenes
Source: VCEasy.org

The first reaction happens at room temperature. If you have a gaseous alkene like ethene, you can bubble it through either pure liquid bromine or a solution of bromine in an organic solvent like tetrachloromethane. The reddish-brown bromine is decolourised as it reacts with the alkene.

(2) Addition polymerisation of alkenes
Source: Chemhume.co.uk

Chemguide links

Chemguide is an excellent revision resource that goes a little further than VCE. Read the relevant Chemguide pages below.

http://www.chemguide.co.uk/organicprops/alkanemenu.html
http://www.chemguide.co.uk/organicprops/alkenemenu.html
http://www.chemguide.co.uk/organicprops/estermenu.html

10.3 Oxidising ethanol to ethanoic acid

You will need to memorise the following ways to oxidise an alkanol into a carboxylic acid.

3 ways to oxidise alcohols
Source: VCEasy.org

For more information, visit this Chemguide page.

10.4: Making Esters

Table of Esters and their Smells
Click to enlarge

10.5: Organic Reaction Pathways

making esters from alkenes
Source: VCEasy.org

10.6: Fractional distillation

Fractional distillation can be used to separate compounds with different boiling points. It is commonly used in the separation of the compounds contained within crude oil.

More information about fractional distillation can be found here.

When hydrochloric acid is added to propene, two products can be produced: 1-chloropropane and 2-chloropropaneOnly the 1-chloropropane can be made into a carboxylic acid. We must therefore separate the 1-chloropropane from the 2-chloropropane by fractional distillation.

When reacting alkenes with 3 or more carbons (such as propene) with hydrochloric acid, we must write “HCl and fractional distillation” on the arrow.

For example:

propane fractional distillation
Source: Heinemann Chemistry 2

Click here for a 4-minute explanatory video about fractional distillation (beyond the VCE Chemistry course).

Read: Heinemann Chemistry 2 Chapter 10

Table of Organic Compounds and their Smells: revised edition

Thanks to the thorough, kind and extremely useful feedback I’ve received as a result of making this chart, I’ve created a revised edition of the Table of Organic Compounds and their Smells poster with 8 additions and corrections. See details underneath.

Table of organic compounds and their smells W12
Click to download PDF version

Additions

  • I found a really old botany book that says undecan-2-one smells like “rue wort”. I don’t know what “rue wort” is, but I’ve labelled it on the chart anyway.
  • Added a 15-carbon row, which includes tamarind, celery and musk smells.
  • Added a benzene row, which includes almonds, tar and orange smells.
  • Added methene, CH₂! It’s extremely unstable and is usually called ‘carbene’. Nobody knows what it smells like because it reacts before it reaches your nose.

Corrections

  • Pentane now has a smell
  • Alkenes are now labelled ‘unpleasant’
  • Corrected the second ketone column header from “2-methyl-” to “methyl-“
  • Moved kumquats to the left.

There were also some minor aesthetic changes: skull & crossbones symbol shows high toxicity (category I or II), while a warning symbol shows moderate toxicity (category III). A green face icon represents a highly unpleasant smell.

Again, thank you to all the people who emailed or otherwise messaged me with feedback on this poster. It pleases me to see how much this poster’s been shared around the internet on many different platforms. I’m glad you find it interesting. 🙂

Book: Organic Chemistry I

Organic Chemistry I
All you need, in theory.

Systematic and super-concise. If only I could take all this in at once.
160 pages, ★★★★

Organic Chemistry I is the most concise guide to organic chemistry I’ve ever found.

The reality is, though, that you’ll have to spend a lot of time using the methods described in this book before they’ll finally sink in.

It would work well as a pre-exam study aid, or as a pre-university Chemistry refresher (as it is for me).

It only lacks the fifth star is because there’s too much to take in at once. While it’s possible to summarise all of Organic Chemistry into a 160-page book, it’s impossible to learn that much simply by reading it. Despite appearances, this book is no replacement for hours of classes, lab experiments, homework tasks and writing assignments. You’ll still need to go to school. ★★★★