Crystalline modifications of cellulose. Part II. A study with plane‐polarized infrared radiation

The bands due to stretching of OH groups in celluloses I, II and III I have been studied with plane polarized infrared radiation. The spectra show that all three crystalline modifications contain OH groups which make an angle much smaller than 55° with the chain direction, while other OH groups make angles greater than 55° with this direction. The former OH groups are attributed to intramolecular hydrogen bonds which join successive glucose residues in the cellulose chain. It is shown that ether oxygen atoms must participate in the hydrogen‐bonding systems in all three modifications. The symmetries of the cellulose chains and the relationship between the two chains in the unit cell are discussed in relation to the number of distinguishable OH groups. Structures are described which are in agreement with the infrared results and with the stereochemical considerations presented in Part III of this series. The frequencies of the bands due to intramolecular hydrogen bonds suggest that the chains in cellulose I have a different molecular form from those in celluloses II and III I . This difference may not be very large, however, in relation to the accuracy with which polymer structures are normally determined.