Arrange them in the increasing -I effect:--C triple bond N , -CH double bond NH , -CH2 - NH2

To arrange the given groups in terms of their increasing -I (inductive) effect, we first need to understand what the -I effect is. The inductive effect refers to the electron-withdrawing or electron-donating properties of substituents attached to a carbon chain. The -I effect specifically indicates that a group pulls electron density away from the rest of the molecule, which can influence reactivity and stability.

Identifying the Groups

Let's break down the groups you provided:

• C≡N (cyano group): This group consists of a carbon triple-bonded to a nitrogen atom. It is a strong electron-withdrawing group due to the high electronegativity of nitrogen and the nature of the triple bond.
• CH=NH (imino group): This is a carbon double-bonded to a nitrogen atom. While it does have some electron-withdrawing characteristics, it is not as strong as the cyano group.
• CH2-NH2 (amino group): This group features a carbon bonded to a nitrogen that is part of an amine. Amines are generally considered electron-donating groups due to the presence of lone pair electrons on nitrogen.

Ranking the Groups

Now, let’s rank these groups based on their -I effect:

1. CH2-NH2: This group has a +I effect because the nitrogen donates electron density through its lone pair, making it the weakest in terms of -I effect.
2. CH=NH: The imino group has a moderate -I effect. It withdraws some electron density due to the double bond with nitrogen, but not as strongly as the cyano group.
3. C≡N: The cyano group exhibits the strongest -I effect. The triple bond and the electronegativity of nitrogen make it a potent electron-withdrawing group.

Final Arrangement

Putting it all together, the increasing order of the -I effect for the groups you provided is:

CH2-NH2 < CH=NH < C≡N

Summary

In summary, the amino group is the weakest electron-withdrawing group, followed by the imino group, and finally, the cyano group, which has the strongest -I effect. Understanding these effects is crucial in predicting the behavior of molecules in various chemical reactions.