Question

The remaining Alkene mixture is ozonolysed carefully in presence of Zinc and Products are treated with mixture of $NH_2OH$. How many oximes obtained.

• A. 2
• B. 3
• C. 4
• D. 5

Answer 1

Answer: (C)

4

Answer 2

The question describes the ozonolysis of a 'remaining Alkene mixture' followed by treatment of the products with hydroxylamine ($NH_2OH$). Ozonolysis ($O_3$ followed by reductive workup with $Zn/H_2O$) cleaves the carbon-carbon double bond of an alkene and converts the carbon atoms involved in the double bond into carbonyl groups (aldehydes or ketones). Aldehydes and ketones react with hydroxylamine to form oximes. The number of different oximes obtained is equal to the number of different carbonyl compounds formed during ozonolysis.

The question does not specify the composition of the 'remaining Alkene mixture'. However, given the multiple-choice options (2, 3, 4, 5), the mixture must be specific and lead to one of these numbers of oximes. A common set of alkenes encountered in introductory organic chemistry are the C4 alkenes:

1. But-1-ene ($CH_3CH_2CH=CH_2$)
2. cis-But-2-ene ($CH_3CH=CHCH_3$)
3. trans-But-2-ene ($CH_3CH=CHCH_3$)
4. 2-Methylpropene ($(CH_3)_2C=CH_2$)

Let's determine the carbonyl products formed by ozonolysis of each of these alkenes:

1. But-1-ene ($CH_3CH_2CH=CH_2$): Ozonolysis yields propanal ($CH_3CH_2CHO$) and formaldehyde ($HCHO$).
2. cis-But-2-ene ($CH_3CH=CHCH_3$): Ozonolysis yields ethanal ($CH_3CHO$). (Both carbons of the double bond become ethanal).
3. trans-But-2-ene ($CH_3CH=CHCH_3$): Ozonolysis yields ethanal ($CH_3CHO$). (Same product as cis-isomer).
4. 2-Methylpropene ($(CH_3)_2C=CH_2$): Ozonolysis yields propanone ($(CH_3)_2C=O$) and formaldehyde ($HCHO$).

The distinct carbonyl compounds produced from the ozonolysis of this mixture of C4 alkenes are:

• Propanal ($CH_3CH_2CHO$)
• Formaldehyde ($HCHO$)
• Ethanal ($CH_3CHO$)
• Propanone ($(CH_3)_2C=O$)

These are four different carbonyl compounds. Each of these carbonyl compounds will react with hydroxylamine ($NH_2OH$) to form a distinct oxime:

• Propanal + $NH_2OH \rightarrow CH_3CH_2CH=NOH$ (Propanal oxime)
• Formaldehyde + $NH_2OH \rightarrow CH_2=NOH$ (Formaldehyde oxime)
• Ethanal + $NH_2OH \rightarrow CH_3CH=NOH$ (Ethanal oxime)
• Propanone + $NH_2OH \rightarrow (CH_3)_2C=NOH$ (Propanone oxime)

These four oximes are structurally different from each other. Therefore, if the 'remaining Alkene mixture' consists of but-1-ene, but-2-ene (cis and/or trans), and 2-methylpropene, then 4 different oximes are obtained. This matches option (C).

Without the context specifying the 'remaining Alkene mixture', assuming it refers to the complete set of C4 alkenes is the most reasonable approach that yields one of the given options. Other subsets of these alkenes would yield 2 or 3 oximes, which are also options. However, the phrasing "remaining Alkene mixture" often implies a specific, possibly complete, set after some process. The complete set of C4 alkenes is a common mixture encountered in problems. It is unlikely that a mixture yielding 5 oximes would be formed from a simple, common set of starting materials or reactions without further specification. Therefore, the most probable intended mixture is the set of all C4 alkenes.