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آرشیو پست ها
2 991
Typical & value for n → n* transition is:
A) > 10000
B) 1000-5000 C) 100-1000 D) 10-100
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Which transition has the highest molar absorptivity (E)?
a)n → п*
b)n → 0* С) п → п* D) 0 → 0*
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Typical & value for n → n* transition is:
A) < 100
B) 100-500 C) 1000-10000 D) > 50000
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Relation between absorbance and concentration is:
a Exponential
b Inverse c Linear d Logarithmic
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The useful UV region for organic compounds is:
100-200 nm
150-250 nm 200-400 nm 400-700 nm
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In UV-Visible spectroscopy, which absorption band (B-band) is used to identify aromatic compounds, and what are its characteristics?
A. B-band: sharp peak at 200 nm, ε > 10,000
B. B-band: broad band with fine structure between 230–270 nm from π→π* transition of
C. B-band: n→π* transition at 320 nm with ε < 100
D. B-band: sharp peak at 400 nm, ε > 50,000
E. B-band: σ→σ* transition below 200 nm
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A pharmaceutical analyst measures the absorbance of a drug solution and obtains A = 1.325. What is the percent transmittance (%T)?
A. 86.7%
B. 13.3% C. 4.73% D. 95.27% E. 0.473%
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1,3-Butadiene absorbs UV radiation at 217 nm, while ethylene absorbs at 171 nm. The reason 1,3-butadiene absorbs at a longer wavelength is:
A. 1,3-Butadiene has a higher molar mass
B. The HOMO–LUMO energy gap is smaller in the conjugated system
C. Ethylene has more π electrons
D. 1,3-Butadiene is a non-polar molecule
E. The σ→σ* transition dominates in 1,3-butadiene
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Regarding UV-Vis, energy required for the following transitions in decreasing order
a- σ →σ*, η →σ*, π → π*, η →π*
b- n → π*, π→ π*, η → σ*, σ→σ* c- σ →σ*, π →π*, η → σ*, η →π* d- π→ π*, σ→σ*, η→ σ*,
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Absorption of radiation in the UV range attributable to n→n* electronic transitions is
characteristic of compounds
a- Unsaturated carbonyl compounds
b- Aromatic hydrocarbons.
c- Non-conjugated polyenes
d- Conjugated polyenes
e- Halide containing compounds
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What is the value of force constant for HCI 1.63*10-27 Kg, and the observed frequency is
8.67*1013 Hz?
a-4.38 dyn A-1 b-4.83 m dyn Å-¹ c- 8.43 dynes cm-¹ d-483 µm-¹ e-4.83 dynes cm-¹
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The absorptivity of a standard sample is 312 of (1% w/ w/v) a solution measured at a path
length of 1 cm, and the absorbance of the sample was 0.624 at wavelength 254 nm. What is the
concentration of
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-Characteristic absorption of organic compound in UV-Vis. At concentrated solution we have -ve or
+ve deviation which may be due to:
a- Association of the molecules & the formation of the complex.
b- Change in the refracting index of the solution.
c- Only due to association of the molecules
d-The formation of the simple derivative.
e-a & b
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Characteristic absorption of organic compound in UV-Vis. The energy required is the highest one
for:
a- π - π* transition b- n → σ* transition c- n → π* transition d- σ → σ* transition e- σ → π* tran
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Ultraviolet and visible (UV-Vis). The principles of this spectroscopy are:
a- The UV radiation region extends from 0 nm to 450 nm
b- The Spectroscopic Techniques are based on the fact that absorption is directly proportional to the
concentration of the absorbing component
c- Visible radiation region extends from 450 nm to 980 nm.
d- Near UV Region: 200 nm to 1000 nm
e- Far UV Region: below 100 nm studied under vacuum condition
