¹³C NMR shifts for IBS in neutral and acidic solutions.

Position	δ C/ppm
	Neutral	Acidic
2	165.75	174.77
4	77.3	73.3
5	187.53	180.31
6	38.38	38.32
7	27.01	26.71
8	27.01	26.71
9	38.38	38.32
10	44.16	44.99
11	137.41	135.20
12	127.96	128.59
13	130.77	130.99
14	140.51	141.27
15	130.77	130.99
16	127.96	128.59
17	142.93	142.77
18	124.75	124.36
19	131.79	131.59
20	129.11	129.35
21	132.43	132.60
22	131.79	131.81
23	157.1	156.57
28	28.77	28.1
29	28.48	27.52
30	23.14	23.04
31	13.98	13.77