Hydrocarbons ā Class 11 CBSE Chemistry revision notes
A 4-page visual revision sheet for Hydrocarbons, written for Class 11 CBSE Chemistry. Formulas, diagrams and the traps that cost marks, laid out to be read the night before rather than the term before. Free, and it opens inside CapCompass.
Page 1 as PDF
Hydrocarbons in one look
carbon and hydrogen only, and the bond type decides everything else
The three families
- Alkanes: C_nH_2n+2, only single bonds, saturated: mostly unreactive except toward free radicals
- Alkenes / Alkynes: C_nH_2n and C_nH_2n-2: one or more C=C or Cā”C bonds, the pi bond reacts
- Arenes: benzene's ring, C_nH_2n-6 for one ring: a stabilised delocalised system, not simple unsaturation
Degree of unsaturation
- for C_nH_mN_pX_q (O/S don't count)
DoU=2n+2+p-m-q/2
Q. Find the degree of unsaturation of C_6H_8, and suggest one structure that fits.
- use DoU=(2n+2+p-m-q)/2 with n=6, m=8, no N or halogens (p=q=0)
- DoU = (2Ć6+2-8)/2 = (12+2-8)/2 = 6/2
- DoU = 3
Answer: DoU = 3, e.g. 1,3-cyclohexadiene: one ring plus two C=C bonds
Naming and preparing alkanes
- Wurtz reaction: 2 R-X+2Na ā R-R+2NaX, joins two alkyl halides
- works best for making a symmetrical alkane
- decarboxylation: sodium carboxylate heated with soda lime (NaOH+CaO) gives an alkane
- one fewer carbon: R-COONa+NaOH ā R-H+Na_2CO_3
- catalytic hydrogenation (Ni/Pt/Pd) adds H_2 across the pi bond(s), giving the alkane
Alkanes: the one reaction that matters
- free-radical halogenation: X_2+UV light or heat replaces one C-H hydrogen at a time
- initiation: X_2 splits into two X radicals under light
- propagation: a radical abstracts H; the carbon radical grabs X from another X_2
- termination: two radicals combine and the chain stops
- a tertiary C-H is abstracted fastest: its radical is most stable (3Ā° > 2Ā° > 1Ā°)
- so a mix of monohalogenated products forms, not just one
Page 1 of 4. The full sheet, all 4 pages, opens free in the app.
What this Hydrocarbons sheet covers
- The three families
- Alkanes
- Alkenes / Alkynes
- Arenes
- Degree of unsaturation
- for C_nH_mN_pX_q (O/S don't count)
- Naming and preparing alkanes
- Alkanes: the one reaction that matters
- Free-radical chlorination of methane, one propagation cycle
- Alkenes: electrophilic addition
- Markovnikov addition to propene
- Worked: Markovnikov addition to 2-methylpropene
- Alkynes: like alkenes, one step further
- Aromaticity: why benzene doesn't behave like cyclohexatriene
- Electrophilic substitution on benzene
- General formulae and typical reaction, at a glance
- Things to remember before the traps
- Traps that cost marks
- Tricks that save time
How CapCompass uses this sheet
These notes are not a standalone PDF. CapCompass plans Chemistry chapter by chapter against your real exam dates and free hours, and when the plan reaches Hydrocarbons the sheet opens inside the study block itself ā at the page covering the sub-topic that block is on, with the timer still running. Revision arrives at the moment the plan says revise, instead of having to be gone looking for.