25 Forgooten Flashcards
What wa skekeule model of benxne
Ring if 6 carbon atoms joined by ALTERNATE DOUBLE AND SINGLE BONDS
- giving LOCALISED electron density above and below the line connecting carbons as pi orbitals overlapped
3 piece of evidence to disprove ke Keule model
What does this suggest
1) enthalpy change of hydrogenation of benzene is actually less than predicted version of cycle hex 135 triene, which was 3 times the amount of cyclohexene
- this means benzene is more stable than that
2) the bond LENTGH of benzene is all the same instead of the longer single and short double as seen and predicted
3) benzene does not decoloruise bromine water under room temperature , or undergoes any Electrophilic addition reactions
Produced the DELOCLAISED version of benzene
List all the pojtns
- Beznene is a planar ring of 6 carbon atoms
- two of the electrons in each carbon is used to form a sigma bond with two other alternating carbons in the ring, and a third to for, one with a hydrogen atom in the same plane,
- the 4th electron of each carbon sits in a p orbital
- adjacent p orbitals thus overlap, leading to a CONTINOUS ring of electron density type above and below the plane of benzene . This forms a SHSTEM OF PI BONDS
- the electrons are said to be DELOCLAISED
- bond angles area 120° each
Main last two sentences for describing deloclasied model
Forms a ring of DELOCLAISED electron density above and below, forming s system of pi bonds
Electrons are said to be DELOCLAISED
Rules for naming bekenne
When alkyl group less than 7 carbons, alkyl group is prefix, so ethylbenzene, nitrobednen
When alky group abive 7 or functional group, then itsohenyethanone, phenyloctane
Besnlic acid
Benzaldehyde
Phenylamine
Can combine things to make 2 broom methyl benzene etc
Remmeber lowest com inaction, and alphabetical order of parent thing
Reactivity if alkenes vs benzene, why can Alkenes decolorudie bromine and ebnende csn’t
1) in benzene the electron density is DELOCLAISED as a CONTINOUS ring above and below the plane spread over all the carbons . In alkene, the electron density is localised in the pi bond between two carbons
2) for any two carbons on average in benzene, will have a lower electron density than the localised in alkene
3) thus it will induce a weaker deiploe or attract a dipole less, and thus is less susceptible to Electrophilic attack, polarise it less
Benedne electroms are DELOCLAISED I’m a system of pi bonds, whereas in Alkenes theory are localsied in a pi bond
Meaning between any two fabrons on abergae Alkenes have hihjer electron density
Bensne induces a weaker piled attracts snd polarised lesss so resistance to Electrophilic attack is higher and needs extra conditond
Remember about stabilityanf aromatic compounds
Most stable as electron density spread Dover s large place rat her than one area
Thus when become shoe horse, wants to become stable again
Nitration temperature control
Needs come H O3, h2sp4 catlayst which si reformed and 50 °
If 70° then it can substitute again
This is Electrophilic SIBSTITUION (can’t do addition)
What are industrial uses of aromatic compund s!
Make tnt
Dyes
Pharmaceuticals like parade Tom all
Why alkylation used
More reactive than ACYLATION
Mechanism same
Still electiphilic subsition
Producers ketone
Phenols bs alcohols
Solubility
Acidic
Phenols are less soluble than alcohols becaude of. NON POLAR BENZENE RING , more carbons so more energy needed to break these of hydration , less soluble the more carbons
Phenols are more acidic than alcohols, and so will react with NaOH a string base, but less acidic than csbroykic acids, which are still weak, but will react with SODIUM CARBONATE as a test
Phenols and Sodium hydroxide form a SALT AND WATWR
Reactivity of OH
For phenols the Oh has a lone pair of electrons and these will PARTIALLY DELOCALISED into the system of pi bonds, increasing the electron density .
- compared to Beinen, phenol carbons will have higher electron density in avergse, and thus can attract a dipole easier, or induce a stirngef dipole, and so are less resisitve to Electrophilic attack snd csn use favourable conditions
- however Alkenes still delocalised and thus induce a string dipole too
Thus ohenol for bonds ti on and jittejton?
Doesn’t need comic HNO3, just weak
No sulfuric acid catlayst
Room temp
Remember two different positions
Brominatioj
- no halogen carrier
At room tempt can do 3 times 2-4 before no more
How DOES BROMIANTIOJ LOOK LIKE FOR PHENOLS THEN
DECOLOURSIATIAOM OF BROMINE WATER WITH A WHITE PRECIPATE FORMED
Activation and descrivejton grouos
Depending on what group is on the Beinen itself, it will activate or deactivate the bednene ifn, or system of pi bond,s making it easier or less easy to res t with electiphiled
For example the Oh on ohenol activated the benzene ring as the line pair on the O partially delfolaisedincresigm Ed and making it easier to react.
Thus brominatioj of ohenol, Esch and is a deactivirsigm group so after 3 it ends, but for NO2 it’s a bigger we’d group so can only do once
Not the NO2 group DEACTIVSTES the aromatic ring, making it less reactive with elevtiphiles, and so harsher conditions are needed , these are called ELECTRON WITHDRAEING GROUPS TOO, Withdrairng electojf density from the pi dodge,
It can also determine DIRECTJON
