Veeah, you raise an interesting point. The symbol is °C which stands for the temperature unit "degree Celsius". When printed correctly, it will be spaced away from its value as in your example, 100 °C. A period is not associated with this unit. The Nemeth Code calls "C" an abbreviation, but I think by understanding that °C is the full symbol, this topic will make more sense when you are confronted with a transcribing dilemma. Regardless, we have guidelines regarding how to transcribe it.
Printed with a hyphen? That is curious. I have noticed that voice recognition software will often insert a hyphen between a number and what follows. I don't know how this started, or if it is related to your observation. Publishers are free to follow their own typographical rules, but I wonder why it is printed this way in a book that has otherwise been using a space? If you are in possession of a pre-publication copy, that hyphen could be indicating a non-breaking space that wasn't caught yet by their proofreaders. Regardless, we must transcribe what is printed.
My first braille mentor, Connie Risjord, taught us well that a Hyphen Connects (and a dash separates). That distinction helps me figure out what to do in unfamiliar situations. I would transcribe 1-°C just as it is printed (unspaced): #1-^.*",C
In 30.4 J/mol °C, follow print spacing: #30.4 ;,J_/MOL ^.*",C
By the way, °C is known as a "derived" SI unit. The SI base unit of (thermodynamic) temperature is the symbol K (for kelvin). It's complicated. Luckily, all we need to do is TRANSCRIBE WHAT WE SEE IN PRINT regarding spacing with the °C symbol.
If I haven't answered your question, please keep asking. This is a confusing topic.