Calculate the pKa of this conjugate acid. These are two acids that are on the Table that we memorized. (1980) have determined via empirical measurements the $\ce {pk_a}$ s of the conjugate acids of acetamide and benzamide to be $\ce {-0.73}$ and $\ce {-1.54}$ respectively, with an uncertainty of $\ce {0.02}$. HCl is a hydrogen halide with a pKa range of 3 to -10 and NH 3 is most similar to a 1° amine (with R = H) that would have an approximate pKa of 35. The strength of a base is related to the pK a of its conjugate acid as pK b = 14 - pK a. a of its conjugate acid as pK b = 14 - pK a. Cox et al. So, HCl would be the stronger acid. Acetamide is a member of the class of acetamides that results from the formal condensation of acetic acid with ammonia. Notice the inverse relationship between the strength of the parent acid and the strength of the conjugate base. Below are tables that include determined pKa values for various acids as determined in water, DMSO and in the gas Phase. So, HCl is the stronger acid (lower pKa). (b) How much more favorable is deprotonation of acetamide in kcal/mol? Explain why acetamide is so much more acidic than ethyl amine, CH3CH2NH2. Data for bases are presented as pK a values for the conjugate acid, i.e., for the reaction +BH H+ + B In older literature, an ionization constant K b ... NO Acetamide 25 15.1 C 2 H 5 NO 2 Acetohydroxamic acid 8.70 C 2 H 5 NO 2 Nitroethane 25 8.46 C 2 H 5 NO 2 Glycine 1 25 2.35 2 25 9.78 C 2 H 6 N 2 When acetamide is protonated by a strong enough acid, it does not protonate on nitrogen, but at a different basic site. The p K a of acetamide (CH 3 CONH 2) is 16. maryamzahedi68 maryamzahedi68 01/26/2018 Chemistry College Actual conjugate acid of acetamide 1 See answer maryamzahedi68 is waiting for your help. pKa values describe the point where the acid is 50% dissociated (i.e. Step-by-step solution: If you are at least 2.0 pH units above the pKa, then the conjugate base is at least 99% of the total. For strengths of organic acids see E. P. Serjeant and B. Dempsey (eds. Actual conjugate acid of acetamide Get the answers you need, now! At the bottom left of Figure 16.5.2 are the common strong acids; at the top right are the most common strong bases. This tells us that acetamide is actually more basic than benzamide. deprotonated). Add your answer and earn points. the acid. ), Ionization Constants of Organic Acids in Solution, IUPAC Chemical Data Series No. Draw the structure of the actual conjugate acid of acetamide, and explain (resonance) why protonation occurs where it does rather than on nitrogen. Draw the structure for its conjugate base and explain why acetamide is less acidic than CH 3 COOH. The phenol acid therefore has a pK a similar to that of a carboxylic acid, where the negative charge on the conjugate base is also delocalized to two oxygen atoms. solution, and the pKa value of an acid, you can quickly determine whether the conjugate base or conjugate acid predominates. The ketone group is acting as an electron withdrawing group – it is ‘pulling’ electron density towards … It's a pKaH value. a. (a) Draw acetamide, CH3CONH2 (pKa = 17) and its conjugate base (Note: always consider loss of the most acidic H, unless stated otherwise). 23, Pergamon Press, Oxford, UK, 1979. b. They are HCl (pKa = -7) and NH 3 (pKa = 38). Method 2. Method 1. Thus the conjugate base of a strong acid is a very weak base, and the conjugate base of a very weak acid is a strong base. In short, the stronger the acid, the smaller the pKa value and strong acids have weak conjugate bases. The value of 10.63 actually refers to the pKa of the conjugate acid of methyl amine, NOT methylamine itself. If the pH is at least 2.0 pH units below the pKa, then the conjugate acid …