Maybe something like: 

c:\@Work\Perl\monks>perl -wMstrict -le
"my $Hn     = qr{ H (?! [[:lower:]]) \d* }xms;
 my $not_Hn = qr{ (?! $Hn) }xms;
 ;;
 use constant FORMULA => 'HC6H5OHHg2HeBr3H';
 ;;
 my $s = FORMULA;
 print qq{'$s'};
 $s =~ s{ $Hn }''xmsg;
 print qq{'$s'};
 ;;
 $s = FORMULA;
 my @elements = $s =~ m{ $not_Hn [[:upper:]] [[:lower:]]? \d* }xmsg;
 printf qq{'$_' } for @elements;
"
'HC6H5OHHg2HeBr3H'
'C6OHg2HeBr3'
'C6' 'O' 'Hg2' 'He' 'Br3'

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In reply to Re: How to avoid an alphabet and integer next to it in a string? by AnomalousMonk
in thread How to avoid an alphabet and integer next to it in a string? by piscean

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