Is a woman less-obligated in bentching?

Question

In a group of two women and one man, why can they not have a zimun together? If it is because of different levels of obligation, why is a woman less-obligated to bentch? If it's the same obligation, why do so many hold that men should not respond to a women's zimun? Or that in 3 men and 3 women, a man leads?

Closely related: Woman and Zimun: What is the requirement?

Answer 1

Th Shulchan Aruch begins the laws of Zimun by saying "Three that have eaten as one". This sentence captures the essence of Zimun in that the 3 people who make up the Zimun must be one unit. Thus if one of the 3 ate a dairy meal and the others meat, or one ate at a separate table or did not end the meal with the other 2, then they can not be considered one unit since they have not "eaten as one". In the case of women, it is not considered modest for men and women to eat together; therefore, there is nothing to bind them together as one unit. While this reason certainly does not apply to one's wife and children, the rabbis do not make that distinction and, once we disallow men and women from making a Zimun, that includes the situation where the men and women are close relatives.

NOTE: The woman’s obligation in Zimun is very real so in a case where she eats with 3 men she should not leave until she bentches with the Zimun. The case for 3 women who ate together is also a strong one but I think we don't again out of modesty although I am not sure.

Answer 2

The Talmud (Brachot 20b) debates if women are obligated to bentch biblically or rabbinically. It doesn't come to a clear conclusion. The Rambam (Brachot 5:1) and others rule it is a doubt and this is how the Shulchan Aruch (OC 186:1) concludes. Rashi (ibid. sv. או דרבנן) suggests that the Talmud considered that women might be exempt biblically from bentching because the verse which is the source for bentching states (Deut 8:10):

וְאָכַלְתָּ, וְשָׂבָעְתָּ--וּבֵרַכְתָּ אֶת-יְהוָה אֱלֹהֶיךָ, עַל-הָאָרֶץ הַטֹּבָה אֲשֶׁר נָתַן-לָךְ‏
And thou shalt eat and be satisfied, and bless the LORD thy God for the good land which He hath given thee

and we know that the women were not accounted for in the initial division of the land. (Even the daughters of Tzlofchad were only claiming their father's portion.)