Peculiarities of NMR ¹³C Spectra of Alkyl Groups in Functionalized Linear Alkanes of the General Formula ch₃(CH₂)_mY

Literary data of NMR ¹³C spectra of linear alkanes X-(CH2) _n-Y (I), (X = H; Y - 38 different substituents, including H and CH₃) were considered. The universal way to estimate the chemical shifts of the methylene groups (δ^C_CH2 = δ^C_i, i = 1 ÷ 36) in I was proposed. It is based on the concept that considers changes in the values δ^C_i of each carbon atom in I (called as increments Δδ^C_i) as a result of conversion to I of a hypothetical alkane with an infinitely long chain -(CH₂)_k-(CH₂)_n-(CH₂)_l- (II) by replacing infinitely long fragments -(CH₂)_k- and -(CH₂)_l- of it with the substituents X and Y. The values δ^C_i of each methylene group in II are assumed the same and equal to that of the medium methylene groups in long-chain alkanes (29.75 ppm). Equal to or greater than 0.05 ppm values of Δδ^C_i increments are observed in only r closest to the X and s closest to Y carbon atoms in the H-(CH₂)_r-(CH₂)_t-(CH₂)_s-Y (I). Parameter r = 5 is a constant, but the parameter s = 4 ÷ 9 is variable, depending on the nature of the substituent Y. Value δ^C_t = 29.75 ppm is constant. All Δδ^C_i increments for each substituent Y are calculated using the formula: Δδ^C_i = δ^C_i - 29.75 ppm, and tabulated. Relationship between the parameters r, s and t determines the length of alkyl chain. All compounds I conditionally divided into three groups: long-chain (n> r + s + t), medium-chain (n