Spec 2

Question 1

What does longer Lambda max indicate

Answer 1

more conjugated system

Question 2

What does change in Lambda max after adding base or acid indicate

Answer 2

presence of ionisable groups

Question 3

what is red shift

Answer 3

• this is when conjugation increases and longer wavelength absorbed (lower energy UV absorbed)

Question 4

what is blue shift

Answer 4

• this is when conjugation decreases and shorter wavelength absorbed (higher energy UV)

Question 5

chromophores define

Answer 5

these a group of multiple/single bond + lone pairs responsible for absorbing UV

Question 6

Auxochrome

Answer 6

functional groups that attach to chromosphore increase their conjugation this causes red shift

Question 7

what happens with electrons when UV aborbed

Answer 7

shift from HOMO to LUMO
the shorter the gap between HOMO to LUMO the more easier the transition so less energy required for transition so a longer wavelength is absorbed ( longer wavelength indicate lower UV energy). This indicates more conjugated system

Question 8

Which type electrons absorb most and least UV energy

Answer 8

pi to pi= absorbs least energy so its most conjugated

n (non bonding) to pi = absorbs most energy this transition is forbidden but happens very rarely

Question 9

what does the molar extinction factor indicate

Answer 9

the intensity of Uv absorption the higher the more compatible HOMO- LUMO (shorter gap transition with ease) so greater wavelength absorbed the more conjugated the system

Question 10

Which has greater lambda max

both chromophore have 5 conjugated atoms

Answer 10

the one that is less electronegative would have greater lambda max as if more electronegative this prevents movement of electrons in conjugated system

trend of electronegativity
F–> O—> N—> C

Question 11

How does increase in unsaturatedness imapct UV absorption

Answer 11

more unstaurated the more conjugated so longer wavelength will be absorbed