5 Improved formatting. edited Mar 12 at 16:51 andselisk♦ 22.3k88 gold badges7878 silver badges149149 bronze badges It's a good idea to start with some data. The table below shows relevant $$\ce{^1H}$$ shifts in $$\pu{ppm}$$ for three compounds in various deuterated solvents (shift values are from Cambridge Isotope Labs): methanol (MetOH), formic acid (FormAc) and ethanoic or acetic acid (AcAc). $$\begin{array}{|c|c|c|c|c|c|} \hline \text{Compound} & \ce{CDCl3} & \ce{(CD3)2SO} & \ce{C5D5N}\; or \; \ce{C5H5N} & \ce{C6D6} \; or \; \ce{C6H6} & \ce{D2O} \\ \hline \text{Acetic acid} & 2.13 & 1.95 & 2.13 & 1.63 & 2.16\\ \hline \text{Formic acid} & 8.02 & 8.18 & 8.54 & 7.24 & 8.22\\ \hline \text{Methanol} & 3.48 & 3.20 & 3.57 & 3.09 & 3.35\\ \hline \end{array}$$$$\begin{array}{|c|c|c|c|c|c|} \hline \text{Compound} & \ce{CDCl3} & \ce{(CD3)2SO} & \ce{C5D5N}\;\text{or}\;\ce{C5H5N} & \ce{C6D6}\;\text{or}\;\ce{C6H6} & \ce{D2O} \\ \hline \text{Acetic acid} & 2.13 & 1.95 & 2.13 & 1.63 & 2.16\\ \hline \text{Formic acid} & 8.02 & 8.18 & 8.54 & 7.24 & 8.22\\ \hline \text{Methanol} & 3.48 & 3.20 & 3.57 & 3.09 & 3.35\\ \hline \end{array}$$ The protons in methanol are more deshielded than those in ethanoic acid because in methanol an electron withdrawing oxygen atom is directly bonded to the carbon, while in ethanoic acid there is an intervening carbon. If you remove that intervening carbon things get interesting, as the case of formic acid illustrates. The carbon atom in a carboxylic group is $$\mathrm{sp^2}$$ hybridized, which makes it more electrophilic than the $$\mathrm{sp^3}$$ hybridized carbon in methanol. Of course the carbon in a carboxylic group is also bound to two electron withdrawing oxygen atoms, rather than one, which results in greater deshielding. The formic acid proton is also subject to deshielding magnetic anisotropy associated with the delocalized electrons of the carboxylic group. The anisotropy effect is less pronounced in ethanoic acid because the methyl group is further away from the carboxylic group. The ultimate result is that the formic acid proton is very strongly deshielded compared to protons in the other compounds. It's a good idea to start with some data. The table below shows relevant $$\ce{^1H}$$ shifts in $$\pu{ppm}$$ for three compounds in various deuterated solvents (shift values are from Cambridge Isotope Labs): methanol (MetOH), formic acid (FormAc) and ethanoic or acetic acid (AcAc). $$\begin{array}{|c|c|c|c|c|c|} \hline \text{Compound} & \ce{CDCl3} & \ce{(CD3)2SO} & \ce{C5D5N}\; or \; \ce{C5H5N} & \ce{C6D6} \; or \; \ce{C6H6} & \ce{D2O} \\ \hline \text{Acetic acid} & 2.13 & 1.95 & 2.13 & 1.63 & 2.16\\ \hline \text{Formic acid} & 8.02 & 8.18 & 8.54 & 7.24 & 8.22\\ \hline \text{Methanol} & 3.48 & 3.20 & 3.57 & 3.09 & 3.35\\ \hline \end{array}$$ The protons in methanol are more deshielded than those in ethanoic acid because in methanol an electron withdrawing oxygen atom is directly bonded to the carbon, while in ethanoic acid there is an intervening carbon. If you remove that intervening carbon things get interesting, as the case of formic acid illustrates. The carbon atom in a carboxylic group is $$\mathrm{sp^2}$$ hybridized, which makes it more electrophilic than the $$\mathrm{sp^3}$$ hybridized carbon in methanol. Of course the carbon in a carboxylic group is also bound to two electron withdrawing oxygen atoms, rather than one, which results in greater deshielding. The formic acid proton is also subject to deshielding magnetic anisotropy associated with the delocalized electrons of the carboxylic group. The anisotropy effect is less pronounced in ethanoic acid because the methyl group is further away from the carboxylic group. The ultimate result is that the formic acid proton is very strongly deshielded compared to protons in the other compounds. It's a good idea to start with some data. The table below shows relevant $$\ce{^1H}$$ shifts in $$\pu{ppm}$$ for three compounds in various deuterated solvents (shift values are from Cambridge Isotope Labs): methanol (MetOH), formic acid (FormAc) and ethanoic or acetic acid (AcAc). $$\begin{array}{|c|c|c|c|c|c|} \hline \text{Compound} & \ce{CDCl3} & \ce{(CD3)2SO} & \ce{C5D5N}\;\text{or}\;\ce{C5H5N} & \ce{C6D6}\;\text{or}\;\ce{C6H6} & \ce{D2O} \\ \hline \text{Acetic acid} & 2.13 & 1.95 & 2.13 & 1.63 & 2.16\\ \hline \text{Formic acid} & 8.02 & 8.18 & 8.54 & 7.24 & 8.22\\ \hline \text{Methanol} & 3.48 & 3.20 & 3.57 & 3.09 & 3.35\\ \hline \end{array}$$ The protons in methanol are more deshielded than those in ethanoic acid because in methanol an electron withdrawing oxygen atom is directly bonded to the carbon, while in ethanoic acid there is an intervening carbon. If you remove that intervening carbon things get interesting, as the case of formic acid illustrates. The carbon atom in a carboxylic group is $$\mathrm{sp^2}$$ hybridized, which makes it more electrophilic than the $$\mathrm{sp^3}$$ hybridized carbon in methanol. Of course the carbon in a carboxylic group is also bound to two electron withdrawing oxygen atoms, rather than one, which results in greater deshielding. The formic acid proton is also subject to deshielding magnetic anisotropy associated with the delocalized electrons of the carboxylic group. The anisotropy effect is less pronounced in ethanoic acid because the methyl group is further away from the carboxylic group. The ultimate result is that the formic acid proton is very strongly deshielded compared to protons in the other compounds. 4 Improved formatting. edit approved Mar 12 at 16:51 Mathew Mahindaratne 11.3k22 gold badges1414 silver badges3939 bronze badges It's a good idea to start with some data. The table below shows relevant $$\ce{^1H}$$ shifts in $$\pu{ppm}$$ for three compounds in various deuterated solvents (shift values are from Cambridge Isotope Labs): methanol (MetOH), formic acid (FormAc) and ethanoic or acetic acid (AcAc). $$\begin{array}{|c|c|c|c|c|c|} \hline \textrm{Compounds} & \ce{CDCl3} & \ce{(CD3)2SO} & \ce{C5D5N} or \ce{C5H5N} & \ce{C6D6} or \ce{C6H6} & \ce{D2O} \\ \hline \textrm{Acetic acid} & 2.13 & 1.95 & 2.13 & 1.63 & 2.16\\ \hline \textrm{Formic acid} & 8.02 & 8.18 & 8.54 & 7.24 & 8.22\\ \hline \textrm{Methanol} & 3.48 & 3.20 & 3.57 & 3.09 & 3.35\\ \hline \end{array}$$$$\begin{array}{|c|c|c|c|c|c|} \hline \text{Compound} & \ce{CDCl3} & \ce{(CD3)2SO} & \ce{C5D5N}\; or \; \ce{C5H5N} & \ce{C6D6} \; or \; \ce{C6H6} & \ce{D2O} \\ \hline \text{Acetic acid} & 2.13 & 1.95 & 2.13 & 1.63 & 2.16\\ \hline \text{Formic acid} & 8.02 & 8.18 & 8.54 & 7.24 & 8.22\\ \hline \text{Methanol} & 3.48 & 3.20 & 3.57 & 3.09 & 3.35\\ \hline \end{array}$$ The protons in methanol are more deshielded than those in ethanoic acid because in methanol an electron withdrawing oxygen atom is directly bonded to the carbon, while in ethanoic acid there is an intervening carbon. If you remove that intervening carbon things get interesting, as the case of formic acid illustrates. The carbon atom in a carboxylic group is $$\mathrm{sp^2}$$ hybridized, which makes it more electrophilic than the $$\mathrm{sp^3}$$ hybridized carbon in methanol. Of course the carbon in a carboxylic group is also bound to two electron withdrawing oxygen atoms, rather than one, which results in greater deshielding. The formic acid proton is also subject to deshielding magnetic anisotropy associated with the delocalized electrons of the carboxylic group. The anisotropy effect is less pronounced in ethanoic acid because the methyl group is further away from the carboxylic group. The ultimate result is that the formic acid proton is very strongly deshielded compared to protons in the other compounds. It's a good idea to start with some data. The table below shows relevant $$\ce{^1H}$$ shifts in $$\pu{ppm}$$ for three compounds in various deuterated solvents (shift values are from Cambridge Isotope Labs): methanol (MetOH), formic acid (FormAc) and ethanoic or acetic acid (AcAc). $$\begin{array}{|c|c|c|c|c|c|} \hline \textrm{Compounds} & \ce{CDCl3} & \ce{(CD3)2SO} & \ce{C5D5N} or \ce{C5H5N} & \ce{C6D6} or \ce{C6H6} & \ce{D2O} \\ \hline \textrm{Acetic acid} & 2.13 & 1.95 & 2.13 & 1.63 & 2.16\\ \hline \textrm{Formic acid} & 8.02 & 8.18 & 8.54 & 7.24 & 8.22\\ \hline \textrm{Methanol} & 3.48 & 3.20 & 3.57 & 3.09 & 3.35\\ \hline \end{array}$$ The protons in methanol are more deshielded than those in ethanoic acid because in methanol an electron withdrawing oxygen atom is directly bonded to the carbon, while in ethanoic acid there is an intervening carbon. If you remove that intervening carbon things get interesting, as the case of formic acid illustrates. The carbon atom in a carboxylic group is $$\mathrm{sp^2}$$ hybridized, which makes it more electrophilic than the $$\mathrm{sp^3}$$ hybridized carbon in methanol. Of course the carbon in a carboxylic group is also bound to two electron withdrawing oxygen atoms, rather than one, which results in greater deshielding. The formic acid proton is also subject to deshielding magnetic anisotropy associated with the delocalized electrons of the carboxylic group. The anisotropy effect is less pronounced in ethanoic acid because the methyl group is further away from the carboxylic group. The ultimate result is that the formic acid proton is very strongly deshielded compared to protons in the other compounds. It's a good idea to start with some data. The table below shows relevant $$\ce{^1H}$$ shifts in $$\pu{ppm}$$ for three compounds in various deuterated solvents (shift values are from Cambridge Isotope Labs): methanol (MetOH), formic acid (FormAc) and ethanoic or acetic acid (AcAc). $$\begin{array}{|c|c|c|c|c|c|} \hline \text{Compound} & \ce{CDCl3} & \ce{(CD3)2SO} & \ce{C5D5N}\; or \; \ce{C5H5N} & \ce{C6D6} \; or \; \ce{C6H6} & \ce{D2O} \\ \hline \text{Acetic acid} & 2.13 & 1.95 & 2.13 & 1.63 & 2.16\\ \hline \text{Formic acid} & 8.02 & 8.18 & 8.54 & 7.24 & 8.22\\ \hline \text{Methanol} & 3.48 & 3.20 & 3.57 & 3.09 & 3.35\\ \hline \end{array}$$ The protons in methanol are more deshielded than those in ethanoic acid because in methanol an electron withdrawing oxygen atom is directly bonded to the carbon, while in ethanoic acid there is an intervening carbon. If you remove that intervening carbon things get interesting, as the case of formic acid illustrates. The carbon atom in a carboxylic group is $$\mathrm{sp^2}$$ hybridized, which makes it more electrophilic than the $$\mathrm{sp^3}$$ hybridized carbon in methanol. Of course the carbon in a carboxylic group is also bound to two electron withdrawing oxygen atoms, rather than one, which results in greater deshielding. The formic acid proton is also subject to deshielding magnetic anisotropy associated with the delocalized electrons of the carboxylic group. The anisotropy effect is less pronounced in ethanoic acid because the methyl group is further away from the carboxylic group. The ultimate result is that the formic acid proton is very strongly deshielded compared to protons in the other compounds. 3 deleted 8 characters in body edited Mar 12 at 13:43 Buck Thorn 6,06322 gold badges88 silver badges3434 bronze badges It's a good idea to start with some data. The table below shows relevant $$\ce{^1H}$$ shifts in $$\pu{ppm}$$ for three compounds in various deuterated solvents (shift values are from Cambridge Isotope Labs): methanol (MetOH), formic acid (FormAc) and ethanoic or acetic acid (AcAc). $$\begin{array}{|c|c|c|c|c|c|} \hline \textrm{Compounds} & \ce{CDCl3} & \ce{(CD3)2SO} & \ce{C5D5N} or \ce{C5H5N} & \ce{C6D6} or \ce{C6H6} & \ce{D2O} \\ \hline \textrm{Acetic acid} & 2.13 & 1.95 & 2.13 & 1.63 & 2.16\\ \hline \textrm{Formic acid} & 8.02 & 8.18 & 8.54 & 7.24 & 8.22\\ \hline \textrm{Methanol} & 3.48 & 3.20 & 3.57 & 3.09 & 3.35\\ \hline \end{array}$$ The protons in methanol are more deshielded than those in ethanoic acid because in methanol there is an electron withdrawing oxygen atom is directly bonded to the carbon, whereaswhile in ethanoic acid there is an intervening carbon in ethanoic acid. If you remove that intervening carbon things get interesting, as the case of formic acid illustrates. The carbon atom in a carboxylic group is $$\mathrm{sp^2}$$ hybridized, which makes it more electrophilic than the $$\mathrm{sp^3}$$ hybridized carbon in methanol. Of course the carbon in a carboxylic group is also bound to two electron withdrawing oxygen atoms, rather than one, which results in greater deshielding. The formic acid proton is also subject to deshielding magnetic anisotropy associated with the delocalized electrons of the carboxylic group. The anisotropy effect is less pronounced in ethanoic acid because the methyl group is further away from the carboxylic group. The ultimate result is that the formic acid proton is very strongly deshielded compared to protons in the other compounds. It's a good idea to start with some data. The table below shows relevant $$\ce{^1H}$$ shifts in $$\pu{ppm}$$ for three compounds in various deuterated solvents (shift values are from Cambridge Isotope Labs): methanol (MetOH), formic acid (FormAc) and ethanoic or acetic acid (AcAc). $$\begin{array}{|c|c|c|c|c|c|} \hline \textrm{Compounds} & \ce{CDCl3} & \ce{(CD3)2SO} & \ce{C5D5N} or \ce{C5H5N} & \ce{C6D6} or \ce{C6H6} & \ce{D2O} \\ \hline \textrm{Acetic acid} & 2.13 & 1.95 & 2.13 & 1.63 & 2.16\\ \hline \textrm{Formic acid} & 8.02 & 8.18 & 8.54 & 7.24 & 8.22\\ \hline \textrm{Methanol} & 3.48 & 3.20 & 3.57 & 3.09 & 3.35\\ \hline \end{array}$$ The protons in methanol are more deshielded than those in ethanoic acid because in methanol there is an electron withdrawing oxygen atom directly bonded to the carbon, whereas there is an intervening carbon in ethanoic acid. If you remove that intervening carbon things get interesting, as the case of formic acid illustrates. The carbon atom in a carboxylic group is $$\mathrm{sp^2}$$ hybridized, which makes it more electrophilic than the $$\mathrm{sp^3}$$ hybridized carbon in methanol. Of course the carbon in a carboxylic group is also bound to two electron withdrawing oxygen atoms, rather than one, which results in greater deshielding. The formic acid proton is also subject to deshielding magnetic anisotropy associated with the delocalized electrons of the carboxylic group. The anisotropy effect is less pronounced in ethanoic acid because the methyl group is further away from the carboxylic group. The ultimate result is that the formic acid proton is very strongly deshielded compared to protons in the other compounds. It's a good idea to start with some data. The table below shows relevant $$\ce{^1H}$$ shifts in $$\pu{ppm}$$ for three compounds in various deuterated solvents (shift values are from Cambridge Isotope Labs): methanol (MetOH), formic acid (FormAc) and ethanoic or acetic acid (AcAc). $$\begin{array}{|c|c|c|c|c|c|} \hline \textrm{Compounds} & \ce{CDCl3} & \ce{(CD3)2SO} & \ce{C5D5N} or \ce{C5H5N} & \ce{C6D6} or \ce{C6H6} & \ce{D2O} \\ \hline \textrm{Acetic acid} & 2.13 & 1.95 & 2.13 & 1.63 & 2.16\\ \hline \textrm{Formic acid} & 8.02 & 8.18 & 8.54 & 7.24 & 8.22\\ \hline \textrm{Methanol} & 3.48 & 3.20 & 3.57 & 3.09 & 3.35\\ \hline \end{array}$$ The protons in methanol are more deshielded than those in ethanoic acid because in methanol an electron withdrawing oxygen atom is directly bonded to the carbon, while in ethanoic acid there is an intervening carbon. If you remove that intervening carbon things get interesting, as the case of formic acid illustrates. The carbon atom in a carboxylic group is $$\mathrm{sp^2}$$ hybridized, which makes it more electrophilic than the $$\mathrm{sp^3}$$ hybridized carbon in methanol. Of course the carbon in a carboxylic group is also bound to two electron withdrawing oxygen atoms, rather than one, which results in greater deshielding. The formic acid proton is also subject to deshielding magnetic anisotropy associated with the delocalized electrons of the carboxylic group. The anisotropy effect is less pronounced in ethanoic acid because the methyl group is further away from the carboxylic group. The ultimate result is that the formic acid proton is very strongly deshielded compared to protons in the other compounds. 2 added 177 characters in body edited Mar 12 at 11:06 Buck Thorn 6,06322 gold badges88 silver badges3434 bronze badges 1 answered Mar 12 at 10:25 Buck Thorn 6,06322 gold badges88 silver badges3434 bronze badges