What's wrong with my command? [duplicate]

This command is being run in Minecraft 1.12:

/summon falling_block ~ ~1 ~ {Block:repeating_command_block,Data:1,TileEntityData:{TrackOutput:0b,Command:execute @a ~ ~ ~ execute @e[type=ender_pearl,r=5,c=1] ~ ~ ~ teleport @p ~ ~ ~},Time:1,Passengers:[{id:falling_block,Block:chain_command_block,Data:1,TileEntityData:{TrackOutput:0b,Command:execute @a ~ ~ ~ kill @e[type=ender_pearl,rm=1,r=5]},Time:1}]}

The command block returns with:

Data tag parsing failed: Expected '}' but got '@' at: ...a:      {TrackOutput:0b,Command:execute @<--[HERE]

What is wrong with this?

You are missing some quotes on the command arguments. After both instances of Command: there should be quotes containing the commands.

This runs successfully:

/summon falling_block ~ ~1 ~ {Block:repeating_command_block,Data:1,TileEntityData:{TrackOutput:0b,Command:"execute @a ~ ~ ~ execute @e[type=ender_pearl,r=5,c=1] ~ ~ ~ teleport @p ~ ~ ~"},Time:1,Passengers:[{id:falling_block,Block:chain_command_block,Data:1,TileEntityData:{TrackOutput:0b,Command:"execute @a ~ ~ ~ kill @e[type=ender_pearl,rm=1,r=5]"},Time:1}]}