Q10-9P-b. - Organic Chemistry (Mcmurry)

Question

Question: How strong a base would you expect a Grignard reagent to be? Look at Table 9-1 on page 276, and predict whether the following reactions will occur as written. (The ${\mathrm{pK}}_{\mathrm{a}}$ of ${\mathrm{NH}}_3$ is 35.)

(b) 

Step-by-Step Solution

Answer

Answer

Yes, the given reaction will occur as written.

Step 1: Grignard reagent

A Grignard reagent is formally the magnesium salt, ${\mathrm{R}}_3{\mathrm{C}}_{21}\mathrm{MgX}$, of a carbon acid, ${\mathrm{R}}_3\mathrm{COH}$, and is thus a carbon anion, or carbanion

Step 2: pK a

It describes the acidity and measures the strength of an acid. Low value of  means, high strength of an acid.

Step 3: Given reaction

From ${\mathrm{pK}}_{\mathrm{a}}$ table, NH₂-H has a ${\mathrm{pK}}_{\mathrm{a}}$value of 35. ${\mathrm{NH}}_3$ is a stronger acid, whereas  ${\mathrm{NH}}_2$ ⁺:is a very weak base, having base strength lower to alkynyl Grignard reagent.

The reaction will occur as written: