When working with acidified food recipes for boiling water canning you
can substitute lemon juice for vinegar in recipes. You cannot
substitute vinegar for lemon juice. Lemon juice has more acid than
vinegar. No conversion is available.

Green tomatoes and tomatillos can be substituted for ripe tomatoes in
any recipe. They are more acidic. Ripe tomatoes cannot be
substituted for green tomatoes or tomatillos in recipes.

Brian Nummer, PhD
National Center for Home Food Preservation
http://www.homefoodpreservation.com