• The blessing of sons comes from Parshat
This is not an isolated situation. It happens with many CHIRIKs followed by a letter with a SH'VA. If the Letter with the CHIRIK also has a METEG, and a YUD would be something not out of place as far as the root of the word and/or form (BINYAN), then the METEG upgrades the CHIRIK and NAs the SH'VA that follows. The same goes for a KUBUTZ (that's the three dots in a diagonal line), which is a short vowel, like the CHIRIK CHASEIR. When the KUBUTZed letter has a METEG, then it behaves as if there is a SHURUK (the VAV with a dot in it), which is a long vowel. This to will NA the SH'VA that follows.
This is an extremely complex issue in DIKDUK and there different opinions about many words that have a METEG followed by a SH'VAed letter.
For now (I expect feedback from the heavy-hitters who frequent this column), let's repeat what started it all. Y'SI-M'CHA ELOKIM... This is not only an issue for the Torah reading of VAI-CHI, but for everyone who blesses his sons, sons-in-law, grandsons, etc. For girls, by the way, the word is straightforward: Y'SI-MEICH...
• B'reishit 49:3 - r'u-VEIN b'CHO-ri A-ta. The last two words are both MIL'EIL. The next word is ko-CHI, which is MILRA.
• In 49:25 is the word v'ya-Z'RE-ka. The AYIN has a SH'VA NACH, which we Ashkenazim don't pronounce, but it still has an effect on the pronunciation of the word. The SH'VA under the ZAYIN is NA and belongs to the second syllable. Avoid saying v'yaz-RE-ka, because that would throw away the AYIN, which shouldn't be done. Even if you don't hear the AYIN (because you don't sound it), the AYIN/SH'VA closes the first syllable v'ya and the second syllable begins with the ZAYIN and its SH'VA NA. Also, the last syllable is "ka", not "cha", because there is a DAGESH in the KAF-SOFIT.
• In 50:17 we find one of the not so common instances where a word is neither MIL'EIL nor MILRA. It is the word ANA, which has two TROP marks. The NUN has a DAGESH in it, with results in emphasizing the NUN. The second syllables TROP is more drawn out, but the bottom line is that both syllables are accented, without favoring either one.
• And getting back to the first word of the sedra and its name... The first syllable is VAI and the second syllable is CHI. The YUD with a SH'VA NACH belongs with the VAV/PATACH. VAI. And the CHET has a CHIRIK MALEI, CHI. The word is not VA - Y'CHI. Even though that's what many of us grew up calling it. In the transliteration of the sedra's name (see below and on the bottom of every page), the Y has been dropped in favor of an I. VAI-CHI, not VAYCHI. The dash can probably be dropped leaving VAICHI, but is there to ease the pronunciation.