OG unit 2.5 Hydrocarbons Flashcards
Well if u seem concerned, go see the first few pages if ya want
Okay
What are free radicals?
Atoms/groups of atoms which have a single unpaired electron
How are free radicals formed?
What name for it?
Bond splits evenly - each atom having one of the 2 electrons
Homolytic fission
What are the 3 stages of Homolytic fission?
Stage 1 - Initiation
Stage 2 - Propagation
Stage 3 - Termination
Explain intitiation stage?
UV radiation causing a [chlorine-chlorine] bond to split homolytically
(symbol for radical is that full stop on the top right of it) aka
Cl]-[Cl (U.V)-> Cl˙ + Cl˙ OR Cl2 (UV)-> 2CL˙ (Chlorine radicals)
Explain propagation stage?
Radicals = reactive ∴ take part in a series of propagation reactions
CH4 + Cl˙ -> ˙CH3 + HCl
CH3 + Cl2 -> CH3Cl + ˙Cl
There’s a diagram for dat one too + chain reaction type sh forming radical as a product
Explain termination stage?
Cl˙ + Cl˙ -> Cl2
Cl˙ + ˙CH3 -> CH2Cl
˙CH3 + ˙CH3 -> CH3CH3
Propagation will continue until two radicals meet = termination
How are alkenes more reactive than alkanes?
- Alkenes more electron density
- Due to more electrons as there are 2 electron pairs = 4 electrons
- Centred between carbons either side of double bond
How can alkenes form bonds?
- Can use one electron pair in double bond
- To react and form new bonds to each carbon atom
What happens to alkanes when their one electron pair is used?
- Sigma bond broken
- Molecule destroyed
U also gotta look at page 6 for them reactivity of alkene n alkane n stuff
Okay
Explain how alkenes give rise to pi bonds?
And ig what that means too?
In the carbon bond:
- As second bond (second pair of electrons) created
- Overlap of p-orbitals of the 2 carbon atoms take place
- Forms pi bonds (area of high electron density)
- Above and below plane of molecule
THAT’S WHY, it’s a double bond
Or just go to page 7 for alkenes related bonding thing
Okay
skip skip skip skip
What it mean for carbon-carbon double bonds having restricted rotation?
- No free rotation due to pi-bond
- Therefore even tho it’s the same molecules,
- It’s a different thing due to it’s position
- That’s why carbon-carbon single bonds would still have the same name despite different position of molecules
Define electrophile?
Atom (or group of atoms) attracted to an electron-rich centre/atom. Accepts a pair of electrons to form new covalent bond
E.g. Hbr/HCl/Cl2/Br2/H
Define nucleophile?
Chemical that can donate a pair of electrons with the subsequent formation of a covalent bond
E.g (All molecules except H have 2 dots above em, lone pair type sh)
-OH, Br-, Cl-, -CN/H2O or NH3
Define free radical?
Atom/group of atoms with an unpaired electron
E.g. ˙Cl, ˙CH3, ˙CH2CH3
What 2 types of addition reactions ig?
- Bromination
- Hydrogenation
4 MAIN THINGS needed to be shown in the model diagram of a reaction between an alkene and some rando ahh molecule?
(4 things)
- Curly arrows
- Dipoles
- Lone pairs
- Charges (full)
MAKE SURE U LOOK AT THESE PAGES FOR EASY 4 MARKS
Look at the page for beginning of section G - Electrophilic Addition. ,’:D
Yikes man…
For bromination, test for what? and how to tell if certain thing present?
- Test for alkenes and presences of C=C double bonds
- Bromine water will decolourise if C=C present
What’s hydrogenation as well?
- H added to alkenes, to saturate them
- Forms alkanes
Explain how u know if it’s a carbocation?
And how u know which ones more stable?
- Propane? But there’s a positive ion? at the bottom of either Carbons.
e.g. 1° - carbocation, 2° - carbocation, etc. lol - 1° is more stable, 3° is less.
Additionally, 1° - carbocation has that positive ion on the bottom right, 3rd carbon :v
But in general how to tell which carbocation stable?
Uhhhh, more alkyl groups attached??? (CH3 or CH2CH3)
- Alkyl groups donate electron density to carbocation, helps stabilise
What u use to test for alkenes? How so?
- Potassium manganate(VII) solution
- Cold state, colour depends based on acidic/alkaline conditions
Show differences in potassium manganate(VII) solution based on acid/alkali
Acidified (dilute sulphuric acid) = Purple solution -> Colourless
Alkaline (sodium carbonate solution) = Purple solution -> Dark green -> Dark brown precipitate
What’s the ick with potassium manganate(VII) solution tho?
- Could give same results from the alkaline solution
It may contain a carbon-carbon double bond. But equally it could be any one of a large number of other compounds all of which can be oxidised by manganate(VII) ions under alkaline conditions
Aye man, u gotta be aware of carbocations n stuff, like is the addition of HBr to propene n stuff, and u can tell if it’s stable or not
Bruhhh
What is addition polymerisation?
Addition reaction that continues until actively stopped
Biology fr
What can be used for monomers adding together toe form long chain polymers?
(2 things)
- Alkenes
- Substituted alkenes
The polymer doesn’t contain double bond, BUT, what is added to the name n stuff showing that it probably does?
- Poly added to monomer
- To involve ene
e.g.
ethene -> polyethene
Make sure u know how to draw a monomer, how to show it’s a repeat unit?
Square brackets [LOL]
Describe what happens to ethene molecules during the formation of polyethene
(3 marks)
- Double bond breaks (1)
- Electron pair forms a new covalent bond,
on a carbon from a neighbouring (ethene) molecule (1) - Forming a saturated polymer chain (1)
And ye, definitely look at the last page, and for sure, ya gotta do some exam questions
Okayyyy
