Why do alkynes have lower pka

Justify your answers, briefly. No, The p K a of ethanol is similar to the pKa of water so proton exchange is comparable for both protonation and deprotonation between alcohols and water. Alcohols can be considered "alkylated water" and share many similarities in both physical properties and chemical reactivity.

Yes, very well. There is a difference of 11 p K a units between the p K a of water and the p K a of acetic acid. The equilibrium lies well to the right with acetate as the predominate form of the original acetic acid. No, hardly at all. The hydroxide ion is too weak a base to remove a proton from acetylene. Studying in Grade 6th to 12th?

Registration done! Sit and relax as our customer representative will contact you within 1 business day Continue. Forum Inorganic Chemistry Q. Why alkyne are more acidic than Why alkyne are more acidic than alkane.

Mohd Mujtaba, 4 years ago. Enter email id Enter mobile number. Cancel Notify me. Sanjana 16 Points. Recall that, all other things being equal, a hydrogen tends to be more acidic when attached to a more electronegative atom.

This is because the conjugate base will be more stable when the negative charge is localized on a more electronegative atom. Unable to load video. Please check your Internet connection and reload this page.

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Recall that the lower the p K a , the stronger the acid. Thus, terminal alkynes are more acidic than other hydrocarbons. Among ethane, ethylene, and acetylene, acetylene is 10 26 more acidic than ethane, and 10 19 stronger than ethylene. What makes terminal alkynes more acidic than alkanes or alkenes? The answer lies in the relative stability of the carbanions formed by deprotonation of the corresponding hydrocarbon. This stability depends on the nature of the hybridized orbital on the negatively charged carbon.

In ethane, the lone pair resides in an sp 3 orbital, while in ethylene it occupies the sp 2 orbital, and an sp orbital in acetylene. Since s orbitals are closer to the positively charged nucleus than p orbitals, electrons in a hybrid orbital with a higher " s " character will experience stronger electrostatic attraction.

Therefore, the acetylide anion will be the most stable and readily formed in the presence of a suitable base. Terminal alkynes have a p K a of Here, the base chosen is such that its conjugate acid has a p K a of at least With sodium amide as the base, terminal alkynes form sodium acetylide and ammonia as the conjugate acid. Since the p K a of ammonia is greater than 35, the equilibrium favors the formation of sodium acetylide, making sodium amide a suitable base for the deprotonation reaction.

In contrast, sodium hydroxide forms water as its conjugate acid. Since the p K a of water is less than 35, the equilibrium favors the reactants. Therefore, terminal alkynes cannot be deprotonated using sodium hydroxide. The strength of an acid is commonly expressed in units of p K a — the lower the p K a , the stronger the acid.

Among the hydrocarbons, terminal alkynes have lower p K a values and are, therefore, more acidic. For example, the p K a values for ethane, ethene, and acetylene are 51, 44, and 25, respectively, as shown here. With a p K a difference of 26 units, acetylene is 10 26 times more acidic than ethane.

Similarly, a difference of 19 p K a units makes it 10 19 times stronger than ethene. The pronounced increase in the acidity of terminal alkynes relative to the other hydrocarbons can be explained by considering the stability of the corresponding carbanions formed by deprotonation.

Note that, in the nomenclature of organic compounds, the suffix "-ide" indicates that the molecule is a negatively charged ion. The stability of the carbanion depends on the nature of the hybridized orbital occupied by the lone pair of electrons. As shown above, in ethane the lone pair resides in an sp 3 orbital, while in ethene it occupies the sp 2 orbital and an sp orbital in the case of acetylene.