Converting Line Bond Structures to Condensed Formulas

Line-Bond Structures In a Line-Bond structure, every atom and every bond is drawn in. The only thing not shown would be any lone pairs on atoms like oxygen or nitrogen or a halide. Show all lines and all letters.

Condensed to Line-Bond Structures Just add in all of the lines. Read the condensed formula from left to right. For example: CH 3 CH 2 CH 3 has three carbons, the left with three H’s, the middle with two H’s and the right with three H’s:

Line Bond structures are detailed… It takes a bit of time to draw one of these! We can simplify our drawing of the molecule using condensed formulas.

Condensed Formulas A condensed formula is actually a Line-Bond structure that has had its lines removed. Shown below is a Line-Bond structure. To convert to a condensed formula, remove the lines… Start with the lines to H’s…

Condensed Formulas Doesn’t matter which end you start from. Just for reference, these are numbered. Notice that C 1 has three hydrogen atoms attached. C 1 can be condensed to CH 3 Notice the same for C 2 – also a CH 3

Condensed Formulas So now re-write the formula, without the lines to H’s: Then remove the last line between the C’s:

Condensed Formulas Did you see how that left hand C 1 suddenly flipped around from H 3 C- to CH 3 -? Most condensed formulas start off with atoms that are NOT hydrogen atoms. Before the line was removed, it was better to keep the line connecting the two C’s (the bond IS between the two C’s, after all…) Don’t worry about this for now… it takes time to build that “intuition”…

Converting to a condensed formula Try this one: Tackle the carbons one at a time…

Converting to a condensed formula Take off the lines to H’s: Then remove the C-C bonds:

Try something “branched” This one doesn’t have just a straight chain. There are four carbons in a row with a branch on the second one from the left (shown in red). Take off those lines to H’s first.

Try something “branched” Remove the lines to H’s: Then remove the C-C lines. Start with those that go straight across:

Try something “branched” There’s still one line left. That’s a “branch”. Because it’s a branch, its okay to leave that one line in the condensed formula. That line shows where the branch is attached.

Using Parentheses Alternatively, we can use parentheses in condensed formulas for branches. Since the second carbon (CH) has TWO CH 3 groups attached to it (exactly the same group, color doesn’t matter), we combined them together in parentheses.

Using Parentheses There are a few things to remember when using Parentheses in a condensed formula. When found on the left end of a formula, the groups are bonded to the NEXT carbon outside the parentheses:

Using Parentheses When found on the right end of a formula, the groups are bonded to thePREVIOUS carbon outside the parentheses:

Using Parentheses And finally, when found in the middle of a formula, the group(s) are bonded to the PREVIOUS carbon outside the parentheses:

Using Parentheses Always double check that you aren’t violating the octet rule: Those two CH 3 groups in the parentheses are both bonded to the C (shown in green), which also has a C on the left (in red) and a C on the right (in blue). FOUR bonds for every C – no more, no less.

Using parentheses… Write the condensed formula for: Start with the lines to H’s…

Using parentheses… Take out all of the lines to H’s: Then remove the C-C lines…

Using parentheses… Now see you have, before using parenthesis: Now, toss in those parentheses… The Br group first…

Using parentheses… The C-Br bond can be removed – Br in parentheses AFTER the CH: Then those THREE CH 3 groups can all come together into a single set of parentheses…

Using parentheses… Leaving you with: Watch the connectivity – parentheses in the middle and on the right end:

One more time… Condense as much as possible! Take out all of the lines to H’s…

One more time… Even the O-H line can go: Now, take out the C-C lines…

One more time… Two lines to two branches left… Use parentheses for the OH…

One more time… One line to one more branch is left… Use parentheses for the last branch…

One more time… Instinctively, you want to put that branch, in parenthesis, right after that CH, don’t you? Good job… BUT… do you see that you actually have TWO CH 2 CH 3 units at the end, on the right?

One more time… With two of the same groups on the same C, they should be in parentheses together! Condense some more!!

One more time… Final Answer: = CH 3 CH(OH)CH(CH 2 CH 3 ) 2

Condensed, Line-Bond, Condensed…. Practice makes perfect… and then you can move on to Skeletal Structures… Go find the PowerPoint “Drawing Skeletal (Zig- Zag) Structures” to head to the next level…