The resonance effect is defined as 'the polarity produced in the molecule by the interaction of two `pi`-bonds or between a `pi`-bond and lone pair of electrons present on an adjacentatom.' The effect is transmitted through the chain.
In positive resonance effect, the transfer of electrons is away from an atom or substituent group attached to the conjugated system. This electron displacement makes certain positions in the molecule of high electron densities. In negative resonance effect, the transfer of electrons is towards the atom or substituent group attached to the conjugated system.
Which of the following does not show resonance effect ?

Options

A. Buta-1, 3-diene
B. Acrylonitrile
C. Nitrobenzene
D. Isopropylisothiocyanate

Explanation

To determine which of the given compounds does not show resonance effect, we need to analyze each compound based on the definition of resonance and the structure of the compounds.

### Step-by-Step Solution:

1. **Understand the Resonance Effect**:
- The resonance effect involves the interaction of pi bonds or between a pi bond and a lone pair of electrons on adjacent atoms.
- Positive resonance effect (or +R effect) involves electron donation away from a substituent, while negative resonance effect (or -R effect) involves electron withdrawal towards a substituent.

2. **Analyze the Options**:
- **Option A: Buta-1,3-diene (CH2=CH-CH=CH2)**:
- Structure: This compound has alternating double bonds (pi bonds) which can interact with each other.
- Resonance: The pi electrons can shift, allowing for resonance structures to form. Therefore, buta-1,3-diene shows resonance.

- **Option B: Acrylonitrile (CH2=CH-C≡N)**:
- Structure: This compound has a double bond adjacent to a triple bond (nitrile).
- Resonance: The electronegative nitrogen can pull electron density, allowing for resonance structures. Thus, acrylonitrile also shows resonance.

- **Option C: Nitrobenzene (C6H5-NO2)**:
- Structure: Nitrobenzene has a nitro group (-NO2) attached to a benzene ring.
- Resonance: The nitro group is an electron-withdrawing group, and resonance can occur between the pi system of the benzene and the nitro group. Therefore, nitrobenzene shows resonance.

- **Option D: Isopropyl isothiocyanate (C3H7-NCS)**:
- Structure: This compound has an isopropyl group attached to an isothiocyanate group.
- Resonance: The arrangement of the bonds does not allow for resonance as there are no alternating double bonds or lone pairs adjacent to pi bonds. Thus, isopropyl isothiocyanate does not show resonance.

3. **Conclusion**:
- After analyzing all options, the compound that does not show resonance effect is **Isopropyl isothiocyanate**.

### Final Answer:
**Isopropyl isothiocyanate does not show resonance effect.**