Here is a list of changes between successive Scheme standards:
Removed in R3RS: -1+, 1+, <=?, <?, =?, >=?, >?, append!, named-lambda, object-hash, object-unhash, rec, sequence, string-null?, string=?, substring-fill!, substring-move-left!, substring-move-right!
Added in R3RS: boolean?, delay, denominator, force, numerator, procedure?, quasiquote, sqrt
Removed in R4RS: exactness, fix, flo, heur, int, last-pair, nil, polar, radix, rat, rect, sci, t
Added in R4RS: list?, peek-char, string
Removed in R5RS: (nothing)
Added in R5RS: call-with-values, define-syntax, dynamic-wind, eval, interaction-environment, let-syntax, letrec-syntax, null-environment, port?, scheme-report-environment, values, call-with-values, define-syntax, dynamic-wind, eval, interaction-environment, let-syntax, letrec-syntax, null-environment, port?, scheme-report-environment, values