शीर्षक: अमीन अभ्यास 13
Answer:
(i) The pKb of aniline is more than that of methylamine due to the presence of the phenyl group in aniline. The phenyl group is electron-donating, which increases the electron density on the nitrogen atom in aniline. This in turn decreases the basicity of the nitrogen atom in aniline, resulting in a higher pKb value compared to methylamine.
(ii) Ethylamine is soluble in water whereas aniline is not due to the difference in their polarity. Ethylamine is a primary amine and has a polar amino group (-NH2) which can form hydrogen bonds with water molecules, making it soluble in water. On the other hand, aniline has a nonpolar phenyl group (-C6H5) attached to the amino group, which decreases its polarity and hinders the formation of hydrogen bonds with water molecules. This lack of hydrogen bonding leads to the insolubility of aniline in water.
(i) Ethanoic acid into methanamine: Ethanoic acid can be converted into methanamine through the following steps:
- Ethanoic acid reacts with thionyl chloride (SOCl2) to form acetyl chloride.
- Acetyl chloride reacts with methylamine (CH3NH2) in the presence of a base, such as pyridine, to yield methanamine.
(ii) Hexanenitrile into 1-aminopentane: Hexanenitrile can be converted into 1-aminopentane through the following steps:
- Hexanenitrile undergoes hydrolysis with aqueous acid (such as HCl) to yield the corresponding carboxylic acid, 1-aminohexanoic acid.
- 1-aminohexanoic acid can be decarboxylated by heating with a strong base (such as NaOH) to obtain 1-aminopentane.
(iii) Methanol to ethanoic acid: Methanol can be converted into ethanoic acid through the following steps:
- Methanol undergoes oxidation with an oxidizing agent, such as potassium permanganate (KMnO4), in the presence of an acid, such as sulfuric acid (H2SO4), to form formaldehyde (CH2O).
- Formaldehyde is further oxidized to formic acid (HCOOH).
- Formic acid undergoes oxidation to produce ethanoic acid.
(iv) Ethanamine into methanamine: Ethanamine can be converted into methanamine by heating it with excess methyl iodide (CH3I) in the presence of a strong base, such as sodium hydroxide (NaOH). This reaction is known as the Hofmann rearrangement.
(i) Why are amines less acidic than alcohols of comparable molecular masses? Amines are less acidic than alcohols because in amines, the lone pair of electrons on the nitrogen atom is less available for donation to an acid. This is due to the higher electronegativity of oxygen compared to nitrogen. As a result, the oxygen atom in alcohols is more capable of donating its lone pair of electrons, making alcohols more acidic.
(ii) Why do primary amines have higher boiling point than tertiary amines? Primary amines have higher boiling points than tertiary amines because primary amines can form intermolecular hydrogen bonding between the hydrogen atom bonded to nitrogen and the lone pairs of electrons on the nitrogen atom. This hydrogen bonding increases the strength of the intermolecular forces and requires more energy to overcome, resulting in a higher boiling point. On the other hand, tertiary amines lack a hydrogen atom bonded to nitrogen, so they cannot form intermolecular hydrogen bonding and have weaker intermolecular forces, leading to lower boiling points.
(iii) Why are aliphatic amines stronger bases than aromatic amines? Aliphatic amines are stronger bases than aromatic amines because the lone pair of electrons on the nitrogen atom in aliphatic amines is more available for donating to an acid. This is due to the electron-donating nature of alkyl groups attached to the nitrogen atom, which increase the electron density around the nitrogen atom, making it more nucleophilic and basic. In aromatic amines, the resonance of the aromatic ring decreases the electron density on the nitrogen atom, making it less nucleophilic and less basic compared to aliphatic amines.
(i) एमिनों की उपग्रहणीय तुलनायुक्त मालों की तुलना में अल्कोहल से कम अम्लीय होती हैं क्योंकि एमिनों में नाइट्रोजन परमाणु ऑक्सीजन परमाणु की तुलना में अधिक वैद्युतिकता धारी होता है। इसका अर्थ है कि एमिनों में नाइट्रोजन परमाणु को इलेक्ट्रॉन्स में अधिक आकर्षण होती है अल्कोहल में ऑक्सीजन परमाणु से, जो एमिनों को प्रोटॉन दान करने के लिए कम संभावित बनाता है और इसलिए उन्हें कम अम्लीय बनाता है।
(ii) प्राथमिक एमिन त्वचा बिंदुओं की तुलना में तृतीयक एमिन से अधिक विषमलता होती हैं क्योंकि प्राथमिक एमिन अन्य मोलेक्यूलों के साथ हाइड्रोजन बंध बना सकते हैं, जबकि तृतीयक एमिन नहीं। ये हाइड्रोजन बंध मोलेक्यूलों के बीच इंटरमालैक्यूलर बालों को बढ़ाते हैं, जिससे उबलने का बिंदु ऊंचा होता है।
(iii) सरलवासी एमिन धारक एमिनों से असारोमैटिक एमिन से अधिक मजबूत आधार होते हैं क्योंकि सरलवासी एमिनों में नाइट्रोजन परमाणु पर एक अनिष्ट्रित तारदार परमाणु होता है, जबकि सघनवासी एमिनों में एक विचलनशील इलेक्ट्रॉन प्रणाली होती है। यह अनिष्ट्रित तारदार परमाणु सरलवासी एमिनों को अन्य मोलेक्यूलों से प्रोटॉन स्वीकार करने के लिए अधिक संभावित बनाता है, जिससे वे मजबूत आधार होती हैं।
