aromatics Flashcards
why is c6h5ch2nh2 stronger than a benzene with no2 at the top and ch2 at the bottom
the lone pair of electrons on the n for the second one is more equally spread out which means the electron density at the n will be reduced so less electrons available (for protonation or donation) so it is less basic
one use of phenyl amines is making dyes, give 3 other uses
making cationic surfactants
making hair conditioner
making fabric softener
bond angle in benzene and cyclohexane
120 degrees in benzene, and 109 in cyclohexane
explain the bonding in benzene and the shape of benzene. compare its stability with that of the hypothetical cyclohexa-1,3,5-triene. use data in your answer. (6 marks)
each carbon has 3 covalent bonds, lone electrons in the p orbitals overlap and this leads to delocalisation. This forms a ring of delocalised electrons which helps making benzene stable
benzene is a planar hexagon and the c-c bonds are equall in length.
stability-
expected for cyclohexa is -360 but hydrog for benzene is -208 which is 152kjmol-1 less exothermic and because benzene is lower in energy than cyclo therefore it is more stable.
the enthalpy of hydrogen of cyclo hexa 1,3 di ene is not exactly double that of cyclohexene, suggest a value for it and justify your value
range of -239 to -121.
the double bonds are separated by one single bond, it allows some delocalisation or the overlap of p orbitals.
why the crude oil product was dissolved in the minimum quantity of hot water
why was the solution filtered
why was the flask left to cool at room temp
why was a clean cork used to compress the crystals in the funnel
why did they add a little cold water (poured) through the crystals
hot water- to ensure that crystals would form upon cooling
filtered- to remove any insoluble impurities
flask left to cool- as the yield would be lower if warm
compress crystals- so air passes through the sample not just around it
cold water- to wash away soluble impurities
the melting point of this sample was found to have a slightly lower mp than a data book- suggest the most likely impurity to have caused this low value and suggest an improvement to the method so a more accurate value for the mp can be obtained
water (excess water)
press the sample of crystals between filter papers
simply, in terms of bonding state why benzene is more stable than cyclo hexa 1,3,5 tri ene
due to delocalised electrons
bond lengths in benzene and shape and stability
all roughly 140 in benzene so its not a distorted hexagon but kekules would be as the double bond c=c and single bond c-c is different
All of the carbon-carbon bonds have exactly the samelengths - somewhere between single and double bonds because there are delocalized electrons above and below the plane of the ring, which makesbenzene particularly stable
comparing bond lengths for benzene and kekules structure
benzene= 140 all bonds
cyclohexa blah c-c= a54
cyclohexa c=c =134
The hydrocarbons benzene and cyclohexene are both unsaturated compounds.
Benzene normally undergoes substitution reactions, but cyclohexene normally
undergoes addition reactions.
(a) The molecule cyclohexatriene does not exist and is described as hypothetical.
Use the following data to state and explain the stability of benzene compared with
the hypothetical cyclohexatriene
benzene is more stable than cyclohexa
expected hydrogenation of benzene is -360 but its actually -208 which is +152 kjmol-1 more stable= less exothermic. Because of delocalisation
Explain why amine U is a weaker base than amine W.
Lone or electron pair on N
No marks if reference to “lone pair on N” missing
1
Delocalised or spread into ring in U
1
Less available (to accept protons) or less able to donate (to H+
)
predicting a value for cycohexa 1,3 di ene where the double bonds are closer than 1.4 di ene. why is the enthalpy of hydrogenation of it lower
if lower enthalpy of hydrogenation= more stable more energy used to break bonds
as, the proximity for 1,3 has c=c closer together delocalisation for 1,3 which provides some extra stability for 1,3
when writing a equation for the reaction of a di nitro to make a di phenyl amine
make sure you do [12H] bc theres 2 nitros to reduce and this also forms 4h2o not 2h2o
bond angle in benzene and cyclohexane
benzene= 120 cyclohexane= 109
