Question

How many moles of \(\mathrm{CH}_{3} \mathrm{MgCl}\) is required to completely react with 1 mole of 3,3 -dimethyl penta-1, 4 -dyne?

Short answer

1 mole of \(\mathrm{CH}_{3}\mathrm{MgCl}\) is required to completely react with 1 mole of 3,3-dimethyl penta-1,4-dyne.

Step-by-step solution

Write the balanced chemical equation for the reaction

We start by writing the balanced chemical equation for the reaction between the Grignard reagent (CH3MgCl) and 3,3-dimethyl penta-1,4-dyne: \(\mathrm{CH}_{3}\mathrm{MgCl} + \mathrm{HC}\equiv\mathrm{C}\)-CH(CH3)2-\(\mathrm{C}\equiv\mathrm{CH} \rightarrow \mathrm{CH}_{3}\)-CH2-\(\mathrm{C} \equiv\mathrm{CH}\) You will notice that this reaction is not balanced yet, as the Mg and Cl atoms are missing from the products. MgCl will form a salt with the terminal alkyne hydrogen: \(\mathrm{CH}_{3}\mathrm{MgCl} + \mathrm{HC}\equiv\mathrm{C}\)-CH(CH3)2-\(\mathrm{C}\equiv\mathrm{CH} \rightarrow \mathrm{CH}_{3}\)-CH2-\(\mathrm{C}\equiv\mathrm{CH} + \mathrm{HMgCl}\) Now the reaction is balanced and we can determine the stoichiometry for the reagents.

Determine the stoichiometry of the reaction

From the balanced chemical equation, we can see that 1 mole of CH3MgCl reacts with 1 mole of the alkyne compound 3,3-dimethyl penta-1,4-dyne. This gives us a 1:1 molar stoichiometry for the reacting moles.

Calculate the moles of CH3MgCl needed

We are given that we have 1 mole of 3,3-dimethyl penta-1,4-dyne and we know the stoichiometry of the reaction is 1:1. So, we can now calculate the moles of CH3MgCl required: Moles of CH3MgCl needed = 1 mole of 3,3-dimethyl penta-1,4-dyne × (1 mole CH3MgCl / 1 mole of 3,3-dimethyl penta-1,4-dyne) = 1 mole of CH3MgCl

Conclusion

1 mole of CH3MgCl is required to completely react with 1 mole of 3,3-dimethyl penta-1,4-dyne.

Key concepts

Chemical Stoichiometry

Chemical stoichiometry is pivotal to understanding how reactants are quantitatively consumed and products are generated in a chemical reaction. An analogy often used is following a recipe where ingredients are mixed in precise ratios to achieve the desired outcome. Similarly, in chemistry, you combine reactants in specific proportions guided by the coefficients in a balanced chemical equation.

For the given exercise, stoichiometry becomes indispensable when deducing how many moles of the Grignard reagent, \( \text{CH}_3\text{MgCl} \) you need to react with 1 mole of the alkyne 3,3-dimethyl penta-1,4-dyne. As the reaction follows a 1:1 molar ratio, stoichiometry tells us directly that 1 mole of the Grignard reagent will suffice for 1 mole of the alkyne, ensuring a complete reaction without any leftover reactants.

Balancing Chemical Equations

Balancing chemical equations is like solving a puzzle where each side of the equation must have the same number of atoms for each element. As a rule, matter cannot be created or destroyed in a chemical reaction, known as the Law of Conservation of Mass. This law underpins the requirement for balanced equations.

In the step-by-step solution, you notice the initial equation is not correctly balanced due to missing \( \text{Mg} \) and \( \text{Cl} \) atoms on the product side. The final equation accounts for every atom by including \( \text{HMgCl} \) as a product, aligning with the law. A perfectly balanced equation not only satisfies scientific accuracy but also ensures precise stoichiometric calculations, directly influencing the amount of each substance required in the reaction.

Alkynes

Alkynes are hydrocarbons with at least one carbon-carbon triple bond, characterized by the general formula \( \text{C}_n\text{H}_{2n-2} \) for linear alkynes. These organic molecules are known for their high reactivity due to the triple bond, which serves as an active site for many chemical transformations, including those with Grignard reagents.

In the exercise, 3,3-dimethyl penta-1,4-dyne serves as the alkyne reactant. Grignard reagents, such as \( \text{CH}_3\text{MgCl} \) in our case, are adept at attacking the carbon atom in the alkyne that is less substituted (or has fewer other carbons attached), leading to the formation of new carbon-carbon bonds. This attribute is exploited in synthesizing larger carbon structures from smaller ones, showcasing the significance of alkynes as building blocks in organic synthesis.