“How could the [brass] plates contain whole chapters from Isaiah that had not yet been written? Lehi obtained the plates about 600 B.C., just before the capture of Jerusalem by the Babylonians and the exile of the population to Babylon. Biblical scholars are almost all agreed that the present Book of Isaiah contains some writings by the prophet written pre-Captivity (up to chapter 35 or 39), but that chapters 40 to 66 could not possibly have been written before the Babylonian Captivity, since the situation described in those chapters does not reflect pre-Captivity circumstances. However, the Book of Mormon contains several whole chapters from this so-called Deutero-Isaiah, supposedly copied from the brass plates… Also, many individual passages from Isaiah’s chapters 52 and 55 appear scattered throughout other books in the Book of Mormon.”
Richard Packham, packham.n4m.org/brassplates.htm
NOTE: Isaiah 48-54 are transferred nearly verbatim in the Book of Mormon.