You don't need to worry too much about what it means because it's not specific but it usually means it’s bonded to another carbon or a hydrogen. If it were bonded to anything other than a carbon or hydrogen it would usually specify it, like it does in the other examples where the carbon of interest is bonded to a heteroatom such as N or O. So in the one you've circled it's just showing the typical 13C NMR shifts for a simple alkyl chain, say, ethane, propane, butane etc. Even if those bonds are linked to other carbons instead of hydrogens it's still going to be a simple alkyl compound, even if branched, and that’s not really going to affect the 13C NMR shift much, as 13C NMR shifts are generally more consistent than 1H NMR shifts.
Obviously in the other examples further down, say, the one at the bottom. If that compound is an aldehyde then you know that bond must be to an H, or if it’s a ketone it must be bonded to another C. Basically, those “sticks” are just a bond to “something”, which as I said, unless specified you can just take to be a C or H as neither of these are likely to really affect the chemical shift of the overall functional group.
You don't need to worry too much about what it means because it's not specific but it usually means it’s bonded to another carbon or a hydrogen. If it were bonded to anything other than a carbon or hydrogen it would usually specify it, like it does in the other examples where the carbon of interest is bonded to a heteroatom such as N or O. So in the one you've circled it's just showing the typical 13C NMR shifts for a simple alkyl chain, say, ethane, propane, butane etc. Even if those bonds are linked to other carbons instead of hydrogens it's still going to be a simple alkyl compound, even if branched, and that’s not really going to affect the 13C NMR shift much, as 13C NMR shifts are generally more consistent than 1H NMR shifts.
Obviously in the other examples further down, say, the one at the bottom. If that compound is an aldehyde then you know that bind must be to an H, or if it’s a ketone it must be bonded to another C. Basically, those “sticks” are just a bond to “something”, which as I said, unless specified you can just take to be a C or H as neither of these are likely to really affect the chemical shift of the overall functional group.
Thank you so much, these things are not explained anyone online or in the book so it's so useful to have guys like you on tsr helping out people!!