Conjugated systems Flashcards
what is an angstrom?
10^-10 metres
what are conjugated double bonds?
alternating double and single bonds
what does conjugation produce?
improves stability
changes structure
changes reactivity
spectroscopic behaviours given
what is lycopene?
gives red colour by being conjugated contains antioxidants properties
what are the characteristics of 1,3-butadiene?
double bonds are shorter than single bonds
electrons are delocalised
overlap between C-C bond giving partial double bond
what does resonance hybrid show?
electron delocalisation
resonance stability
extended bond
what is the relationship between conjugation and light absorption?
more conjugated a system the longer the wavelength of light absorbed
show electrophilic aromatic substitution?
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what is the structure of benzene?
all carbons are the same length
they have partial double bonds
pie electrons delocalised around the ring
how is aromaticity predicted?
Huckel’s rule
what is Huckel’s rule?
4n+2= number of pie electrons
how to predict aromaticity using Huckel’s rule?
if n= full number then aromatic molecule
if n= decimal then not aromatic
what molecules does the Huckel’s rule apply to?
planar monocyclic rings
where each atom has a pie orbital
what is the arrehenius definition of acids and bases and why its a limited definition?
acid increases concentration of H+ ions when dissolved in water
base increases concentration of OH- ion when dissolved in water
acid/base reaction is a neutralisation reaction
limited definition because water is needed as a solvent in liquid phase
requires only two ions
what is the Bronsted lowry acid and bases definition and why its limited definition?
acid is a H+ donor
base is a H+ acceptor
limited by H+
always use for aqueous solutions
what is the equation of autoionization of water?
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water both base and acid
what is the lewis acids and bases definition and why its limited definition?
acid accepts an electron pair
base donate electron pair
acid/base reaction creation of a covalent bond
what is a strong and weak acid?
strong acid fully dissolves in water releasing H+ ions
weak acid partially dissolves in water releasing H+ ion
how to determine if an acid-base reaction is in completion or equilibria?
reactions using strong acid or strong base goes to completion and others are in equilibrium
what is Kw at 25 degrees?
the ionisation constant of water
1* 10^-14
what are the rules of autoionization of water?
if concentration of strong acid/base is more than 110^-6 then ignore water autoionization equilibrium
if concentration of strong acid/base is less than 110^-6 then water autoionization equilibrium needs to be acknowledged
what reaction is used for weak acid?
Ka
stronger Ka?
the larger the Ka the stronger the acid
equation of Ka?
[A-]=[H+]
so
[H+]=square root(Ka*[HA])
what is the pH equation for weak acids?
pH= 1/2 pKa -1/2log[HA]
what is the symbol used for weak base?
Kb
equation of Kb?
[OH-]= square root (Kb[B])
therefore:
[H3O+]=Kw/square root(Kb[B])
equation for pKw?
pKw= pKa+pKb
what is the equation of pH for weak bases?
pH=1/2pKw +1/2pKa +1/2log [B]
what is the Henderson Hasselbach equation
pH=pKa +log [A-]/[HA]
what is buffer pH?
‘function of it’s pKa and the ratio of concentrations of anion and acid, but the buffer’s capacity depends upon actual concentrations’
