Instrumental Techniques Spectroscopy

Step 1: Understanding the concept of splitting in NMR.
In NMR, the splitting pattern is determined by the number of adjacent protons (coupling). A triplet occurs when a proton is coupled to two equivalent protons. This will split the signal into three peaks (a triplet), with the coupling constant ( ) determining the spacing between the peaks.

Step 2: Analyzing the compounds.
- **(A)** The compound shows a methylene group ( ) next to a group, which will split the signal into a triplet.

- **(B)** This compound shows two equivalent methyl groups ( ) attached to a carbonyl group, which will not show a triplet.

- **(C)** This compound has a benzene ring and a methyl group, but no adjacent equivalent protons that would cause a triplet.

- **(D)** This compound has a hydroxyl group and a bromine atom attached to the benzene ring, but no protons that would create a triplet pattern.

Step 3: Conclusion.
The correct answer is (A), as it is the only compound that will show a triplet in its NMR spectrum.

Step 1: Analyzing the options.
(A) Absorption occurs at all wavelengths if light passes through a given solution: Incorrect — Absorption occurs at specific wavelengths corresponding to the energy levels of the molecules involved.
(B) The efficiency of a photochemical process is often expressed in terms of quantum yield: Correct — Quantum yield is a measure of the efficiency of a photochemical reaction and is the ratio of the number of molecules reacting to the number of photons absorbed.
(C) The unit of molar extinction coefficient is litre mole cm: Incorrect — The molar extinction coefficient, also called molar absorptivity, is typically expressed in units of .
(D) The extent of absorption in a dilute solution would be the same if the concentration is doubled and the path-length of light passing through solution is halved: Correct — According to Beer-Lambert law, absorbance is directly proportional to both the concentration of the solution and the path length. Doubling the concentration and halving the path length will result in the same absorbance.

Step 2: Conclusion.
The correct answers are (B) and (D).

1. Molecular Formula and Unsaturation

The molecular formula is .

The Index of Hydrogen Deficiency (IHD) is calculated as:

$ \text{C}_5\text{H}_{10}\text{O} C=5, H=10, N=0, X=0 \text{C}=\text{O} \mathbf{1715\ \text{cm}^{-1}} \text{C}=\text{O} 1725\ \text{cm}^{-1} {}^1\text{H NMR} n+1 n 4:6 6:4 n+1=3 \implies n=2 \text{H} \text{CH}_3 \text{CH}_2 n+1=4 \implies n=3 \text{H} \text{CH}_2 \text{CH}_3 \text{CH}_3-\text{CO}-\text{CH}_2-\text{CH}_2-\text{CH}_3 \text{CH}_3 \text{CH}_2 \text{CH}_2 \text{CH}_3 \text{CH}_3-\text{CH}_2-\text{CO}-\text{CH}_2-\text{CH}_3 \mathbf{\text{CH}_3} \mathbf{\text{CH}_2} \text{CH}_3-\text{CO}-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{CH}_3 \text{CH}_3 \text{CH}_2 \text{CH}_2 \text{CH}_2 \text{CH}_3 \text{CH}_3-\text{CO}-\text{CH}(\text{CH}_3)_2 \text{CH}_3 \text{CH}_3 \text{CH} \text{Pentan-3-one} \text{CH}_3^a \text{CH}_2^b \text{H} \text{CH}_2^b \text{CH}_3^a \text{H} {}^1\text{H NMR}$ spectrum.